Add checkbox to automatically run a pipeline when Auto DevOps is turned on in project settings

What does this MR do?

EE MR, https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/3578

• Adds support for automatically running a pipeline after Auto DevOps has been enabled for a project.

Are there points in the code the reviewer needs to double check?

1. I'm not sure if I used subject correctly when cleaning the PipelinesSettingsController. I think I did, but it's worth double-checking.
2. The specs I wrote might be too verbose/detailed. I'm not 100% sure.

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• N/A API support added
• Tests added for this feature/bug
• Review
  • Has been reviewed by UX
  • Has been reviewed by Frontend
  • Has been reviewed by Backend
  • N/A Has been reviewed by Database
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together
• Internationalization required/considered

What are the relevant issue numbers?

Closes #38962 (closed)