Improve docker setup

- add .dockerignore
- add entrypoint.sh to switch to user after initial setup
- downgrade importlib-metadata for Celery compatibility
- add TZ environment variable for consistent Celery timestamps
- fix Celery setting deprecation warnings

entrypoint.sh

@@ -0,0 +1,5 @@
+#!/bin/sh
+
+set -e
+
+su -c /srv/gvapgsql.sh gvapgsql