Code Review Analytics: Add new filtered search bar

What does this MR do?

This MR is part of an ongoing effort towards replacing the filtered search bar with GlfFilteredSearch on the Code Review Analytics page, see #212682 (closed) for details. It fetches milestones and enables users to select the milestone token from the filtered search.

The changes are behind the :code_review_analytics_has_new_search feature flag which is currently disabled until all work has been finished.

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