Attempt to rationalize a bit workers config in docker
- use a common workers.env file for all worker services,
- move services/swh-loaders-worker/entrypoint.sh in services/swh-worker/ and use where possible in docker-compose.yml,
- merge docker/env/statsd.env in common_python.env.
It could be possible to rationalize more, eg. merging all worker entrypoint.sh in a single one.
Migrated from D2433 (view on Phabricator)