[BUG/Feature Request] Parameter to pass the config file

### The use case you're trying to solve

I have 2 flavors and different headers for each flavor. So I have created 2 separate `firebase.json` files. My first approach was to keep these files in the root project directory with separate names. This works if we use `firebase --config=firebase-dev.json deploy` command directly. But for the github actions, we have a param for entryPoint which takes the path where `firebase.json` file can be found.

### Change to the action that would solve that use case

There should be a parameter to pass the config file. Right now, for example, you can use `firebase --config=./firebase-dev.json deploy` command, and it will use `firebase-dev.json` instead of `firebase.json` as config file.

### Other considerations

Other way to solve this problem is to create 2 folders inside your project each containing a separate firebase.json file. Now, the issue is, if we specify entrypoint `./firebase_config/prod`, it successfully fetches the firebase.json file available inside. But now, when it comes to deployment, it tries to find the public folder inside firebase_config/prod and sends error that public folder not found for hosting. So there should be another parameter in the actions `build` which will take the path that needs to be deployed.