BE: Allow customers to extend or reactivate their trial on gitlab.com [RUN ALL RSPEC] [RUN AS-IF-FOSS]

What does this MR do?

Related to issue #290278 (closed)

There are 4 MRs for issue #290278 (closed)

• migration script on Gitlab: !56460 (merged)
• migration script on CustomersDot: https://gitlab.com/gitlab-org/customers-gitlab-com/-/merge_requests/2937
• feature code on Gitlab: !56471 (merged) (this MR)
• feature code on CustomersDot: https://gitlab.com/gitlab-org/customers-gitlab-com/-/merge_requests/2940

Note: the issue's Data requirement has not confirmed yet, so please ignore data requirement during review.

This MR add a put method extend_reactivate in trials controller

• it requires params[:trial_extension_type] as one params
• it validates params[:trial_extension_type] against the namespace
• if the request is valid, it calls GitlabSubscriptions::ExtendReactivateTrialService
• GitlabSubscriptions::ExtendReactivateTrialService will send a put request to CustomersDot

Screenshots (strongly suggested)

Does this MR meet the acceptance criteria?

Conformity

• 📋 Does this MR need a changelog?
  • I have included a changelog entry.
  • I have not included a changelog entry because _____.
• 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 #290278 (closed)

doc/api/audit_events.md

@@ -6,6 +6,8 @@ info: To determine the technical writer assigned to the Stage/Group associated w
 
 # Audit Events API
 
+> [Introduced](https://gitlab.com/gitlab-org/gitlab/-/issues/121) in GitLab 12.4.
+
 ## Instance Audit Events **(PREMIUM SELF)**
 
 The Audit Events API allows you to retrieve [instance audit events](../administration/audit_events.md#instance-events).