[ML] Fix retention of categorization example limits (#182103)

When updating a job's model memory limits via the UI, if
`categorization_examples_limit` has been set in `analysis_limits`, the
configured value is replaced by the default value of `4`.
This appears to be a
[bug](elastic/elasticsearch#108068) in
elasticsearch and so this PR is a workaround to ensure the original
`categorization_examples_limit` is sent as part of the update to ensure
it isn't reset to the default.

Also fixes an issue in the advanced job wizard where setting
`categorization_examples_limit` in the JSON is not retained when saving
the JSON.

x-pack/plugins/ml/public/application/jobs/jobs_list/components/edit_job_flyout/edit_utils.js

@@ -104,6 +104,14 @@ function extractMML(job, newJobData) {
     if (mml !== job.analysis_limits.model_memory_limit) {
       mmlData.analysis_limits = {
         model_memory_limit: mml,
+        // work around for issue in es where categorization_examples_limit will be reset to the default value
+        // if it is not included in the update request
+        // https://github.com/elastic/elasticsearch/issues/108068
+        ...(job.analysis_limits.categorization_examples_limit !== undefined
+          ? {
+              categorization_examples_limit: job.analysis_limits.categorization_examples_limit,
+            }
+          : {}),
       };
     }
   }

x-pack/plugins/ml/public/application/jobs/new_job/common/job_creator/job_creator.ts

@@ -21,6 +21,7 @@ import {
 } from '@kbn/ml-anomaly-utils';
 import type { RuntimeMappings } from '@kbn/ml-runtime-field-utils';
 import type { SavedSearch } from '@kbn/saved-search-plugin/public';
+import { isPopulatedObject } from '@kbn/ml-is-populated-object';
 import type { IndexPatternTitle } from '../../../../../../common/types/kibana';
 import { getQueryFromSavedSearchObject } from '../../../../util/index_utils';
 import type {
@@ -327,11 +328,18 @@ export class JobCreator {
 
   public set modelMemoryLimit(mml: string | null) {
     if (mml !== null) {
-      this._job_config.analysis_limits = {
-        model_memory_limit: mml,
-      };
+      if (this._job_config.analysis_limits === undefined) {
+        this._job_config.analysis_limits = {};
+      }
+      this._job_config.analysis_limits.model_memory_limit = mml;
     } else {
-      delete this._job_config.analysis_limits;
+      if (this._job_config.analysis_limits !== undefined) {
+        delete this._job_config.analysis_limits.model_memory_limit;
+
+        if (isPopulatedObject(this._job_config.analysis_limits) === false) {
+          delete this._job_config.analysis_limits;
+        }
+      }
     }
   }