Sync config with https://gitlab.inf.unibz.it/commul/docker/commons/blob/master/helm-charts/webserver/nginx.conf

Fix #35.

This reverts commit 9717f5b1 because
withwith #35 fixed 'xmlui.session.ipcheck' can be safely used again.

- disabled ssl-passthrough
- configured ssl-certs

FIXME:
- repository/oai is not accessible via http
- battle test the config

Prefix (oai/requeststripped) and add entries in robots.txt.

- sitemaps are now generated in the entrypoint script