[llvm] [GitHub] Add workflows to manage merging of PRs from authors without commit access (PR #124910)

[David Spickett via llvm-commits]

DavidSpickett wrote:

Something like:
* Opened PR without commit access is labelled.
* Workflow notices the PR has been approved.
* Ping approvers to merge the PR, remove the label. From here the workflow ignores the PR.

This ping also include the list of things to check, that I am currently sending to the author. Then if the approver judges it not to be ready then they can reference that list when saying so.

* Either it's merged then, or -
* It's not merged and each subsequent comment discussing that will be a notification to everyone anyway.
* Eventually one of those reminds an approver to merge the PR, or -
* The author is now aware they can request a merge again, since they saw the bot do it before. If that doesn't happen in practice, I can make it explicit in the initial ping that the author can request another look at the PR.

I'll work on a version like this next week.

https://github.com/llvm/llvm-project/pull/124910