Adjust docs for using feature flags for tracking using Redis HLL

What does this MR do?

Adjust docs for using feature flags for tracking using Redis HLL

Use feature flags default enabled false for events trigger automatically or arriving with api or when multiple added in the same time.

Use feature flag default enabled false for events triggered by user

With the current learnings I think we can have this clear in docs when to use feature flag default enabled true or false

Screenshots (strongly suggested)

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 #287785 (closed)