Add logging to importer. Closes issue elastic#192212 (elastic#192234)

## Summary
Hello, this closes issue elastic#192212 by adding a custom logger to the
importer, making debugging issues easier.
### Checklist

Delete any items that are not applicable to this PR.

- [N/A] Any text added follows [EUI's writing
guidelines](https://elastic.github.io/eui/#/guidelines/writing), uses
sentence case text and includes [i18n
support](https://github.com/elastic/kibana/blob/main/packages/kbn-i18n/README.md)
- [N/A]
[Documentation](https://www.elastic.co/guide/en/kibana/master/development-documentation.html)
was added for features that require explanation or tutorials
- [x] [Unit or functional
tests](https://www.elastic.co/guide/en/kibana/master/development-tests.html)
were updated or added to match the most common scenarios TODO
- [ ] [Flaky Test
Runner](https://ci-stats.kibana.dev/trigger_flaky_test_runner/1) was
used on any tests changed TODO
- [N/A] Any UI touched in this PR is usable by keyboard only (learn more
about [keyboard accessibility](https://webaim.org/techniques/keyboard/))
- [N/A] Any UI touched in this PR does not create any new axe failures
(run axe in browser:
[FF](https://addons.mozilla.org/en-US/firefox/addon/axe-devtools/),
[Chrome](https://chrome.google.com/webstore/detail/axe-web-accessibility-tes/lhdoppojpmngadmnindnejefpokejbdd?hl=en-US))
- [N/A] If a plugin configuration key changed, check if it needs to be
allowlisted in the cloud and added to the [docker
list](https://github.com/elastic/kibana/blob/main/src/dev/build/tasks/os_packages/docker_generator/resources/base/bin/kibana-docker)
- [N/A] This renders correctly on smaller devices using a responsive
layout. (You can test this [in your
browser](https://www.browserstack.com/guide/responsive-testing-on-local-server))
- [N/A] This was checked for [cross-browser
compatibility](https://www.elastic.co/support/matrix#matrix_browsers)

### For maintainers

- [X] This was checked for breaking API changes and was [labeled
appropriately](https://www.elastic.co/guide/en/kibana/master/contributing.html#kibana-release-notes-process)
(no API changes)

---------

Co-authored-by: Elastic Machine <[email protected]>
(cherry picked from commit c36a894)

packages/core/saved-objects/core-saved-objects-import-export-server-internal/src/import/saved_objects_importer.ts

@@ -9,6 +9,7 @@
 
 import type { SavedObjectsImportResponse } from '@kbn/core-saved-objects-common';
 import type { SavedObjectsClientContract } from '@kbn/core-saved-objects-api-server';
+import type { Logger } from '@kbn/logging';
 import type {
   ISavedObjectTypeRegistry,
   ISavedObjectsImporter,
@@ -27,15 +28,18 @@ export class SavedObjectsImporter implements ISavedObjectsImporter {
   readonly #typeRegistry: ISavedObjectTypeRegistry;
   readonly #importSizeLimit: number;
   readonly #importHooks: Record<string, SavedObjectsImportHook[]>;
+  readonly #log: Logger;
 
   constructor({
     savedObjectsClient,
     typeRegistry,
     importSizeLimit,
+    logger,
   }: {
     savedObjectsClient: SavedObjectsClientContract;
     typeRegistry: ISavedObjectTypeRegistry;
     importSizeLimit: number;
+    logger: Logger;
   }) {
     this.#savedObjectsClient = savedObjectsClient;
     this.#typeRegistry = typeRegistry;
@@ -46,6 +50,7 @@ export class SavedObjectsImporter implements ISavedObjectsImporter {
       }
       return hooks;
     }, {} as Record<string, SavedObjectsImportHook[]>);
+    this.#log = logger;
   }
 
   public import({
@@ -57,6 +62,7 @@ export class SavedObjectsImporter implements ISavedObjectsImporter {
     compatibilityMode,
     managed,
   }: SavedObjectsImportOptions): Promise<SavedObjectsImportResponse> {
+    this.#log.debug('Starting the import process');
     return importSavedObjectsFromStream({
       readStream,
       createNewCopies,
@@ -80,6 +86,7 @@ export class SavedObjectsImporter implements ISavedObjectsImporter {
     retries,
     managed,
   }: SavedObjectsResolveImportErrorsOptions): Promise<SavedObjectsImportResponse> {
+    this.#log.debug('Resolving import errors');
     return resolveSavedObjectsImportErrors({
       readStream,
       createNewCopies,

packages/core/saved-objects/core-saved-objects-server-internal/src/saved_objects_service.ts

@@ -376,6 +376,7 @@ export class SavedObjectsService
           savedObjectsClient,
           typeRegistry: this.typeRegistry,
           importSizeLimit: options?.importSizeLimit ?? this.config!.maxImportExportSize,
+          logger: this.logger.get('importer'),
         }),
       getTypeRegistry: () => this.typeRegistry,
       getDefaultIndex: () => MAIN_SAVED_OBJECT_INDEX,

src/core/server/integration_tests/saved_objects/routes/import.test.ts

@@ -13,6 +13,7 @@ import supertest from 'supertest';
 import { SavedObjectsErrorHelpers } from '@kbn/core-saved-objects-server';
 import { savedObjectsClientMock } from '@kbn/core-saved-objects-api-server-mocks';
 import type { ICoreUsageStatsClient } from '@kbn/core-usage-data-base-server-internal';
+import type { Logger, LogLevelId } from '@kbn/logging';
 import {
   coreUsageStatsClientMock,
   coreUsageDataServiceMock,
@@ -56,6 +57,17 @@ describe(`POST ${URL}`, () => {
     references: [],
     managed: false,
   };
+  const mockLogger: jest.Mocked<Logger> = {
+    debug: jest.fn(),
+    info: jest.fn(),
+    error: jest.fn(),
+    warn: jest.fn(),
+    trace: jest.fn(),
+    fatal: jest.fn(),
+    log: jest.fn(),
+    isLevelEnabled: jest.fn((level: LogLevelId) => true),
+    get: jest.fn(() => mockLogger),
+  };
 
   beforeEach(async () => {
     ({ server, httpSetup, handlerContext } = await setupServer());
@@ -76,6 +88,7 @@ describe(`POST ${URL}`, () => {
       savedObjectsClient,
       typeRegistry: handlerContext.savedObjects.typeRegistry,
       importSizeLimit: 10000,
+      logger: mockLogger,
     });
     handlerContext.savedObjects.getImporter = jest
       .fn()

src/core/server/integration_tests/saved_objects/routes/resolve_import_errors.test.ts

@@ -12,6 +12,7 @@ jest.mock('uuid');
 import supertest from 'supertest';
 import { savedObjectsClientMock } from '@kbn/core-saved-objects-api-server-mocks';
 import type { ICoreUsageStatsClient } from '@kbn/core-usage-data-base-server-internal';
+import type { Logger, LogLevelId } from '@kbn/logging';
 import {
   coreUsageStatsClientMock,
   coreUsageDataServiceMock,
@@ -61,6 +62,17 @@ describe(`POST ${URL}`, () => {
     references: [],
     managed: false,
   };
+  const mockLogger: jest.Mocked<Logger> = {
+    debug: jest.fn(),
+    info: jest.fn(),
+    error: jest.fn(),
+    warn: jest.fn(),
+    trace: jest.fn(),
+    fatal: jest.fn(),
+    log: jest.fn(),
+    isLevelEnabled: jest.fn((level: LogLevelId) => true),
+    get: jest.fn(() => mockLogger),
+  };
 
   beforeEach(async () => {
     ({ server, httpSetup, handlerContext } = await setupServer());
@@ -82,6 +94,7 @@ describe(`POST ${URL}`, () => {
       savedObjectsClient,
       typeRegistry: handlerContext.savedObjects.typeRegistry,
       importSizeLimit: 10000,
+      logger: mockLogger,
     });
 
     handlerContext.savedObjects.getImporter = jest