feat: create dockerfile for docker hub integration

[jacobheun]

• Adds a Dockerfile to the repo so that we can integrate image builds in libp2p Docker Hub
• Removes Procfile associated with old deployment setup

Additional Fixes

• Use pkg.files instead of .npmignore
• Fix dependency usage of prom-client

Building and running the container

You can build and run the container locally via:

Build: docker build -t libp2p/webrtc-star .
Run: docker run -it -p 9090:9090 --env DEBUG=signalling-server,signalling-server:error libp2p/webrtc-star

TODO:

• Connect libp2p Docker Hub org to this repo: https://hub.docker.com/r/libp2p/js-libp2p-webrtc-star
• Configure master branch and tags

unblocks libp2p infra team deployment of #180

[jacobheun]

@vasco-santos CI is failing due to an unrelated issue with Firefox. I did some local testing and it looks like the recent version of Firefox (74), which came out on March 10 is causing some issues. I verified test failures locally on Firefox 74 and passing test on Firefox 72 (the previous version). I'll create an issue to track fixing this, currently not sure what's causing the issues.

[vasco-santos]

LGTM!