Feat: Allow github actions to use custom configuration #1489

I am playing around with integrating the github action for some of my company repositories and we are not allowed to use raw API key access for models and instead need to do all actions through LiteLLM. It would be nice if we are able to provide a custom configuration option + the ability to specify environment variables to be able to configure the github runner action in the same way the local tool can be used.

I maybe did this backwards by opening a PR first, but I have an implementation open here. Happy to discuss, change, or drop as you see fit:
#1488