[Discover] Split saved searches out of discover plugin

[flash1293]

This PR splits shared saved search logic (used by discover and visualize) out of the discover plugin into a separate plugin. This will allow to implement the histogram in Discover using a Lens embeddable in a later step (otherwise it would have introduced a cyclic dependency).

This PR is mostly moving over the saved search service - react hook and conflict component are left within Discover because they are not used anywhere else.

[kibana-ci]

💚 Build Succeeded

• Buildkite Build
• Commit: 814ae5d

Metrics [docs]

Module Count

Fewer modules leads to a faster build time

id	before	after	diff
discover	555	548	-7
savedSearch	-	11	+11
total			+4

Public APIs missing comments

Total count of every public API that lacks a comment. Target amount is 0. Run node scripts/build_api_docs --plugin [yourplugin] --stats comments for more detailed information.

id	before	after	diff
discover	68	73	+5
savedSearch	-	39	+39
total			+44

Async chunks

Total size of all lazy-loaded chunks that will be downloaded as the user navigates the app

id	before	after	diff
discover	463.1KB	464.2KB	+1.1KB

Public APIs missing exports

Total count of every type that is part of your API that should be exported but is not. This will cause broken links in the API documentation system. Target amount is 0. Run node scripts/build_api_docs --plugin [yourplugin] --stats exports for more detailed information.

id	before	after	diff
discover	7	5	-2
savedSearch	-	1	+1
total			-1

Page load bundle

Size of the bundles that are downloaded on every page load. Target size is below 100kb

id	before	after	diff
discover	29.1KB	25.7KB	-3.3KB
savedSearch	-	4.7KB	+4.7KB
visualizations	46.8KB	46.8KB	+3.0B
total			+1.4KB

Unknown metric groups

API count

id	before	after	diff
discover	84	89	+5
savedSearch	-	39	+39
total			+44

ESLint disabled in files

id	before	after	diff
discover	2	1	-1
savedSearch	-	1	+1
total			-0

Total ESLint disabled count

id	before	after	diff
discover	39	38	-1
savedSearch	-	1	+1
total			-0

History

• 💔 Build #63928 failed 894e7f7
• 💔 Build #63918 failed 44163a4

To update your PR or re-run it, just comment with:
@elasticmachine merge upstream

[elasticmachine]

Pinging @elastic/kibana-data-discovery (Team:DataDiscovery)

[jbudz]

limits.yml

[kertal]

LGTM, code review, testing by merging with the lens in Discover POC, cyclic dependency resolved. thx for taking care of the heavy lifting 👍

[dej611]

Tested locally 👍
Left only a tiny nitpick comment.

[dej611]

nit: can these be merged?

[kertal]

that's what this PR will do ... once the merge conflicts are resolved: #137488
Joe's PR went first, because I doubt he already has grey hair ... while one gray hair more for me, doesn't matter 👴