Similarity search in projects dropdown

What does this MR do?

This MR exposes the similarity_search feature flag to the frontend and when it's enabled, the project dropdown will use the order_by=similarity option when requesting the projects.

Note: since the feature is behind a FF, I didn't create changelog.

Affected project dropdowns: Productivity Analytics and Value Stream Analytics

How to test it:

1. Ensure that you have ultimate license
2. Seed VSA: FILTER=cycle_analytics SEED_CYCLE_ANALYTICS=1 bundle exec rake db:seed_fu
3. Open the generated group and add more projects with similar names, for example: git, gitlab, gitlab-runner
4. Enable the feature flag: Feature.enable(:analytics_similarity_search) AND Feature.enable(:similarity_search) (enabling similarity option for the groups/:id/projects API endpoint)
5. Go the group value stream: analytics / value stream analytics
6. In the project dropdown search for git
7. Top results should be very similar to the search phrase

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