Change Author of Problem Matcher Annotations

[panicstevenson]

Describe the enhancement
It feels like there should be customizability around who is posting the annotations created by problem matchers. For instance, having annotations be created by reponame-ci-bot might feel more familiar to users in a repository that are unfamiliar with GitHub Actions as a whole. I would expect this to be a non-required environment variable, similar to overriding GITHUB_TOKEN with a personal access token, but that doesn't seem to work currently.