Rename InstanceStatistics to UsageTrend [RUN ALL RSPEC] [RUN AS-IF-FOSS]

What does this MR do?

This change renames the instance analytics feature in the codebase. This MR includes:

• Change the route (with backward compatibility)
• Rename files in frontend and backend
• Rename and migrate the background worker queues
• Rename the GraphQL API endpoint and keep the old one (deprecated) for background compatiblity
• Eliminate feature flag for the feature (already enabled by default for while)

Note: The UI strings and documentation have been changed earlier, so does not introduce visible changes.

How to test it

1. Make sure your GDK is seeded
2. Go to admin / analytics / usage trends
3. Charts should show up

Follow ups for 14.0

• Remove the old worker: #321670 (closed)
• Remove the redirect: #321670 (closed)

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

Related to #285438 (closed)