Add a workflow to bump the Homebrew cask version

[MWin123]

Currently, the workflow is triggered manually. If it works as expected, it can be added to the existing "Gradle Build" workflow. Fixes #20.

The workflow ran successfully with my forks, and generated this PR (MWin123/homebrew-esque#2). Unfortunately, the run history from the workflows is gone because I had to create a new fork to submit this PR.

I forked the GitHub action bump-homebrew-formula-action because it doesn't fully work with casks yet, see my open issue (Support for Homebrew Cask). If the author implements a fix, we can switch back to the original version.

The COMMITTER_TOKEN secret is required because this action will want to write to an external repository. You can generate a new PAT here and give it public_repo (or repo if the homebrew tap repository is private) scopes.

It's necessary to create a COMMITTER_TOKEN secret for this repo, see the action's description for details.