Add PR triage workflow

[mumrah]

Replaces #17298.

This patch adds a simple label based workflow for PRs. PRs opened by non-committers will have a triage label automatically added. This allows committers to see which PRs need to be triaged. After 7 days, a needs-attention label will be added. This serves as a reminder to committers and allows them to see which PRs have languished.

For now, the triage label will need to be manually removed by a committer. In the future, we could try to automate this by removing the label after a PR has been reviewed, assigned, or commented on.

[chia7712]

I totally love this idea!

After 7 days, a needs-attention label will be added. This serves as a reminder to committers and allows them to see which PRs have languished.

Could we just add label "needs-attention" if the PRs from non-committer have no reviewer after 7 days? That may be more simple and it can remind committers to check those languished PRs as well

[fvaleri]

I like this, thanks @mumrah.

[mumrah]

@chia7712

Could we just add label "needs-attention" if the PRs from non-committer have no reviewer after 7 days?

Unfortunately, pull_request_reviewed has the same issues as pull_request, but there is no pull_request_reviewed_target event to allow editing details of the PR. I tried a few things, but ultimately don't think we can achieve much automation as the result of a review being submitted :(

So, for now it would be a manual process to remove the triage label. If the triage label is removed, the needs-attention label will not be applied.

One improvement we can make is to use https://github.com/actions/stale?tab=readme-ov-file#exempt-all-pr-assignees to prevent needs-attention from being added if the PR has an assignee. This might not be that useful since we rarely use assignee.

Edit: Since we already require adding ci-approved, it seems that requiring a removal or triage is not too burdensome for committers. After all, it is only a few clicks in the UI :)