Add method to build docker image + use bot without music features and dependencies

[Laura7089]

The music functionality requires one to setup a google developer account, and also increases the size + build time of the docker image. I think it could be desirable to enable one to run the bot without needing the dependencies and the API keys etc.

I see that we have the ENABLE_MUSIC environment variable - it would be pretty trivial to modify our Dockerfile and docker-compose.yml files to use docker multistage builds to enable rapid iteration/testing without having to run apt etc.

[Laura7089]

This could also apply to pip dependencies