[Search] Deprecate search indices in favour of index management

[seialkali]

Summary

This PR deprecates the search_indices plugin in favour of the index management plugin. The following changes were made to facilitate this:

• Deprecates the search_indices plugin's custom index details and create index pages, consolidating all Search solution index management into the shared platform index_management plugin
• Moves the Search index management app registration from search_indices to enterprise_search, which renders the platform index_management plugin's UI within the Search solution layout
• Removes the IndexDetailsPageRoute extension mechanism from index_management that allowed search_indices to override the index details route at runtime
• Introduces a SearchIndexManagementLocator in search_navigation that resolves routes based on chrome style (project vs classic), replacing scattered navigateToApp calls and deep link references across Search plugins
• Updates all Search plugins (search_homepage, search_playground, search_getting_started, search_inference_endpoints, enterprise_search) to use the new locator for index management links
• Updates FTR and Jest tests to validate against platform index_management UI and removes tests/page objects for deprecated search_indices UI

To reduce the number of file changes in this PR, the removal of the search_indices plugin will be done in a separate PR.

Screenshots

Testing

• Navigation -- With the Search solution active, click Data Management in the side nav. Verify it loads at app/management/data/index_management/indices and the nav item is highlighted.
• Index Details -- Create an index and navigate to the index details page. Verify that the page loads with the index management plugin's index details page. See screenshot above.
• Create Index -- Click Create index on the index list. Verify the new modal opens (not a page redirect). Create an index and confirm it appears.
• Context Menu -- Open the context menu for an index. Verify overview/settings/mapping/stats actions navigate correctly. Verify delete works from the manage button on the details page.
• Cross-Plugin Links -- Verify these all navigate to the correct index management pages:
  • Search Playground: Create an index button (shows when there are no indexes)
  • Search Homepage: Data Management card
  • Getting Started: Create an empty index menu item, which is under the Add data button
  • Inference Endpoints: When deleting a custom inference endpoint that's in use by an index mapping, the confirm modal should link to the index and should open in new tab
• Serverless -- Repeat the above in a serverless Search project.

Checklist

Check the PR satisfies following conditions.

Reviewers should verify this PR satisfies this list as well.

• Any text added follows EUI's writing guidelines, uses sentence case text and includes [i18n support](https://github.com/elastic/kibana/blob/main/src/platform/packages/shared/kbn-i18n/README.md)
• Documentation was added for features that require explanation or tutorials
• Unit or functional tests were updated or added to match the most common scenarios
• If a plugin configuration key changed, check if it needs to be allowlisted in the cloud and added to the docker list
• This was checked for breaking HTTP API changes, and any breaking changes have been approved by the breaking-change committee. The release_note:breaking label should be applied in these situations.
• Flaky Test Runner was used on any tests changed
• The PR description includes the appropriate Release Notes section, and the correct release_note:* label is applied per the guidelines
• Review the backport guidelines and apply applicable backport:* labels.

[csr]

AppEx QA codeowner changes LGTM 👍

[delanni]

👍 limits.yml

[macroscopeapp]

Approvability

Verdict: Needs human review

This PR is a major architectural refactor that deprecates the standalone 'search indices' application and consolidates functionality into 'index management'. It introduces new routing/locator patterns, modifies navigation trees, and touches multiple plugins across different team ownership domains. The author does not own any of the modified files, and the cross-cutting nature of these changes warrants review by the designated code owners.

^{You can customize Macroscope's approvability policy. Learn more.}

[elasticmachine]

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[efegurkan]

LGTM.

Checked locally and as extensively as I can.

One thing maybe is to check whether it makes sense to add a state in index management so "create" links can open the modal by default. If so we can try as a separate PR.

[seialkali]

One thing maybe is to check whether it makes sense to add a state in index management so "create" links can open the modal by default. If so we can try as a separate PR.

@efegurkan I thought this as well. Definitely one for the a separate PR, as this one is already a monster!

[leathekd]

Schema lgtm

[mattkime]

changes look good and work well!