Record trial status widget experiment variant assignments

What does this MR do?

Records each top-level Group as they enter into the Trial Status Widget experiment as well as which variant of the experiment the Group received.

Participation in the experiment is limited by the following factors:

• Top-level Groups that are in an active trial
• Owner members of those top-level Groups

Note: The top-level Group and the current user’s membership within that Group are looked up even if the user only navigates to a sub-Group page.

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 #300728 (closed)