IIUC, the recommended approach to using this action with custom base images is to fork or embed and add new Dockerfiles.

Assuming one didn't want additional customization in the Dockerfile beyond an arbitrary base image (which is always the case for the builtins and the custom images I was using), it seems like it'd be pretty straightforward to generate the Dockerfile on the fly from a template to make any base image work with the stock action. eg, add a new optional base_image arg that would be templated into FROM- without the arg, the current behavior against the Dockerfiles in the action, and with it, using a dynamic Dockerfile. This change would obviate the need to fork and customize the action merely for different base images.

Thoughts?