[RUN AS-IF-FOSS] Redis HLL counters on plan/namespace level

What does this MR do?

Add plan level reporting when tracking events using Redis HLL

Add group_by_plan attribute to known_events.yml

Add plan as parameter to track_event method track_event(entity_id, event_name, plan: '', time: Time.zone.now)

Add plan as parameter to unique_events method unique_events(event_names:, start_date:, end_date:, plan: '')

Update related docs.

Next steps

• Create issue for Add the plan level metrics to usage data generation #268268 (closed)
• Create issue for Adjust the controller/helpers methods to accept plan parameter #268269 (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

Related issue #254669 (closed)