Clean up Dockerfile

[dennisvang]

Changes to Dockerfile:

• single (multi-stage) Dockerfile instead of two
• run app as spring user instead of root
• simplified entrypoint and application config files, so we can easily select profile using env variable

fixes #621

[dennisvang]

@MarekSuchanek Not sure if you rely on the separate (single stage) Dockerfile for commit hook or similar?

[MarekSuchanek]

@MarekSuchanek Not sure if you rely on the separate (single stage) Dockerfile for commit hook or similar?

I think the single stage Dockerfile was used in the past for building the Docker image in CI... true that it is not needed anymore.