Docker support config via env vars

[Codycody31]

Changes

• Add a .env.example file for the environmental variables we support
• Add CLI cmd inject-config to return a yaml file with the config containing env vars
• Add docker-compose.yml and update entrypoint.sh script
• Incorporate a script in the UI called generate-yaml.js to generate a new file called ui-config.yaml which is not included in git.

Purpose

This PR now adds support for using environment variables making it way easier to run discuit via docker.

Related Issues

• closes: #45

Requests When Reviewing

I didn't know how the cmd in main.go should be so it is called inject-config but it's most definitely free to be changed to a better name, as the current one was just a test/general and the purpose has changed.