Add a kind of bot that notifies authors about merge conflicts

[thomaseizinger]

Description

Have an automation that comments with something like: Hey @author, please resolve the merge conflicts with the base branch.. We should be able to do that with a GitHub workflow that runs on the synchronize activity of the pull_request event. The mergable property will have the value CONFLICTING if there are any conflicts. To avoid double commenting if a PR already has conflicts, we can set a label or something and exclude the workflow from those PRs.

Motivation

GitHub does not send a notification when a PR has merge conflicts because the base branch changed. Having to manually check one's open PRs or wait for maintainers to pick them up is cumbersome.

Current Implementation

Are you planning to do it yourself in a pull request?

Maybe.

[jxs]

addressed with #3026