Add support for specifying the commit ref in the config file

[andrewrynhard]

No description provided.

[olivernybroe]

This feature is especially handy when it comes to GitHub actions and also in general for sharing the config file with the rest of the team

[andrevalentin]

Yeah this would be perfect, really appreciating all your support. Adding this would save us from using another action for this particular check presently. 💯