Suggestion: Docker container logs as input log

Hello,

Thanks for your work on mtail. I would like to propose a feature that allows users to use logs generated by a Docker container as input for metric generation. Currently, users have two options: either their application must log to a specific file, which means they loose the benefits of having the application's logs within the container logs, or they need to set up an additional sidecar container to create a log file from the Docker API which seems a bit overengineering.

I think it would be possible to embed the docker client library in mtail to use a container logs as input. What do you think of that?

Cheers