Cache ES enabled namespaces and projects

What does this MR do?

A recent postgres-checkup report includes:

SELECT query involving elasticsearch_indexed_projects table consumes >40% of the master resources. The query itself is not slow (13.224 ms/call), but it happens almost 100 times per second.

This MR implements caching of elasticsearch_indexed_projects and elasticsearch_indexed_namespaces.

This cache has a relatively small number of ids and it rarely changes.

#209854 (closed)

Screenshots

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• [-] Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• [-] Tested in all supported browsers
• [-] Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• [-] Label as security and @ mention @gitlab-com/gl-security/appsec
• [-] The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• [-] Security reports checked/validated by a reviewer from the AppSec team