add annotations based on lint failures

[suo]

pytorch/pytorch#64449 removed the add_annotations workflow from the workflow_run trigger, because it causes flakiness (lots of artifact uploading/downloading) and noises up master CI. In its place, we have the lint workflow run the add_annotations action itself.

Sadly, this doesn't work for CI runs triggered by PRs from forked repos, because the GITHUB_TOKEN supplied to fork pull requests only has read permissions.

@seemethere suggested an elegant solution, which is to have probot handle all of this to sidestep the write permission issues.