Add support for custom files to update

[npars]

Is your feature request related to a problem? Please describe.
The image updater currently only catches image tags that are in Dockerfiles in our repo. It would be nice if it also updated
docker-compose files so that we would not need to manually push commits to the PRs that the tool creates.

Describe the solution you'd like
Add ability to search for and update docker-compose yaml files in a addition to Dockerfiles. A basic search might be
something like: language:yaml filename:docker-compose "image: docker/image/name". This will miss files that don't
follow the docker-compose file name convention, but that's probably better than searching all yaml files.

Describe alternatives you've considered
N/A

Additional context
N/A

[afalko]

I'm changing the subject to allow us to pass a list of files we want to scan vs. only supporting Dockerfiles

[afalko]

Also while we do this, we should consider supporting wild cards:
Dockerfile-*

[justinharringa]

We already scan all Dockerfile by virtue of using filename:Dockerfile and it will find, for example Dockerfile-somethingelse

[justinharringa]

I believe you'll need to be somewhat specific about parsing / file format as well.