[Automatic Import] Correctly output icons in the manifest (#201139)

## Release Note

Fixes a bug in Automatic Import where icons were not shown after the
integration was installed.

## Summary

Closes #201008.

When implementing safe manifest output #192316 a bug crept in:
the icons array was incorrectly output as a dictionary

    icons:
      src: /img/logoElastic.svg
      title: syslog_test3 Logo
      size: 32x32
      type: image/svg+xml

and the test was not smart enough to pick it up:

    expect(manifest.icons).toBeTruthy();

We fix the field and add better tests for it.

x-pack/plugins/integration_assistant/server/integration_builder/build_integration.test.ts

@@ -277,6 +277,13 @@ describe('renderPackageManifestYAML', () => {
     expect(manifest.name).toBe(integration.name);
     expect(manifest.type).toBe('integration');
     expect(manifest.description).toBe(integration.description);
-    expect(manifest.icons).toBeTruthy();
+    expect(Array.isArray(manifest.icons)).toBe(true);
+    expect((manifest.icons as object[]).length).toBe(1);
+    expect((manifest.icons as object[])[0]).toEqual({
+      src: '/img/logo.svg',
+      title: 'Sample Integration Logo',
+      size: '32x32',
+      type: 'image/svg+xml',
+    });
   });
 });

x-pack/plugins/integration_assistant/server/integration_builder/build_integration.ts

@@ -185,12 +185,14 @@ function createPackageManifestDict(
   };
 
   if (package_logo !== undefined && package_logo !== '') {
-    data.icons = {
-      src: '/img/logo.svg',
-      title: `${package_title} Logo`,
-      size: '32x32',
-      type: 'image/svg+xml',
-    };
+    data.icons = [
+      {
+        src: '/img/logo.svg',
+        title: `${package_title} Logo`,
+        size: '32x32',
+        type: 'image/svg+xml',
+      },
+    ];
   }
   return data;
 }