Add proper Docker dev environment

[adriansalamon]

Adds a proper dev environment using Docker and docker-compose.

The application relies on serveral third party services that are included in the compose file:

• Postgres
• Login, here we use nyckeln-under-dorrmattan
• AWS S3, here we use minio which is an S3 compatible service
• Imgproxy, just using a local imgproxy instance

This makes it much easier to start development on Haj, and also safer, since we for example don't need access to actual AWS during local development.

This makes major changes to env variables, so need to test that it does not break production deployments.