Add entrypoint scripts for DEV only on first container creation

[minottic]

Entrypoints are run whenever the container is recreated, for example on

docker compose down && DEV=true docker compose up -d

This may override local changes, for example, in the frontend the merge_json.sh script overrides the config.json file which might differ from the merged config.json.

In DEV the entrypoints should be skipped if the container is recreated, for example by checking if the .git directory exists.

[minottic]

closed by #379