Throttle pipelines creation rate

What does this MR do and why?

Related to https://gitlab.com/gitlab-org/gitlab/-/issues/352232

Since we already have a limit for how many active pipelines a project could have, I think it would be a good idea to add a limit on how many pipelines could be created by a user for a commit in a short period of time. This should stop rogue pipelines that the other two limits fail to catch.

This limits the number of pipelines created for the same project/commit/user tuple to 20 per minute. This value is not definitive yet.

Rollout plan

• enable ci_track_throttle_pipelines_creation for a week and monitor the logs
• if there isn't any entry in the log file, proceed to disable ci_throttle_pipelines_creation_dry_run and start enforcing the limit
• if there are log entries, analyze them and reconsider the limit.
• as a follow-up, move the limit into an application_settings column

Screenshots or screen recordings

How to set up and validate locally

1. Run database migrations: bin/rails db:migrate
2. Update the limit to a lower value: ApplicationSetting.current.update!(pipelines_create_limit: 2)
3. Enable the ci_throttle_pipelines_creation feature flag:
   • Feature.enable(:ci_throttle_pipelines_creation)
4. Disable the ci_throttle_pipelines_creation_dry_run feature flag to enforce the limit:
   • Feature.disable(:ci_throttle_pipelines_creation_dry_run)
5. Open 3 tabs on the new pipelines in the same project: namespace/project/-/pipelines/new
6. Press the Run pipeline button in each tab

MR acceptance checklist

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• I have evaluated the MR acceptance checklist for this MR.