Resolve "Track action metrics for a merge request"

What does this MR do?

Related to #292827 (closed)

This merge request is about tracking four actions in relation to a merge request:

Action	Description
created	MR Created
closed	Closed a MR
merged	Merged a MR
reopened	Reopened a MR

Currently we are tracking this information in the events create service, but this will be removed and replaced with these trackings once we have data in these metrics.

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