docker setup

[efstajas]

Adds improved Docker setup:

• New Dockerfile.dockerhub that can be used to build a prod-ready image of graphql-api
• Automatic workflow that uses that Dockerfile to build a prod image and push it to Dockerhub on push to staging or main

Railway still builds without a Dockerfile for now because there was some funkiness.

Todo:

• Adjust README
• Add all other services, app etc. to a docker-compose once all those images are up on Dockerhub

[railway-app]

🚅 Previously deployed to Railway in the Drips App project. Environment has been deleted.