Add API endpoint to manage pipeline settings - specifically 'Auto cancel pending pipelines'
<!--IssueSummary start--> <details> <summary> Everyone can contribute. [Help move this issue forward](https://handbook.gitlab.com/handbook/marketing/developer-relations/contributor-success/community-contributors-workflows/#contributor-links) while earning points, leveling up and collecting rewards. </summary> - [Close this issue](https://contributors.gitlab.com/manage-issue?action=close&projectId=278964&issueIid=18661) </details> <!--IssueSummary end--> Zendesk: https://gitlab.zendesk.com/agent/tickets/79402 Customer would like the ability to manage CI/CD pipeline settings via the API. Specifically, they want to be able to disable the 'Auto cancel pending builds' feature. From what I can see, we don't currently support changing any pipeline settings via the API, but we do support changing other project settings.
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