Add tracking to measure the number of unique users committing CI config

What does this MR do?

This MR adds a tracking event to measure the number of unique users committing to the CI config file.

The track event is sent when;

• The feature flag is enabled.
• The commit target is the main branch of the project.
• The commit includes the main CI config file of the project.
  • We will add the included files in future iterations.

It is behind a feature flag usage_data_unique_users_committing_ciconfigfile (#299403 (closed)).

Related to #293670 (closed)

Screenshots (strongly suggested)

[19] pry(main)> ::Gitlab::UsageDataCounters::HLLRedisCounter.unique_events_data['pipeline_authoring']
=> {"o_pipeline_authoring_unique_users_committing_ciconfigfile_weekly"=>3, "o_pipeline_authoring_unique_users_committing_ciconfigfile_monthly"=>3}
[20] pry(main)> ::Gitlab::UsageDataCounters::HLLRedisCounter.unique_events_data['pipeline_authoring']
=> {"o_pipeline_authoring_unique_users_committing_ciconfigfile_weekly"=>4, "o_pipeline_authoring_unique_users_committing_ciconfigfile_monthly"=>4}

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