DataHUB: correctly configure https

[Zalfsten]

Currently we set the external URL of our DataHUB/gitlab to use the http protocol instead of https. As the TLS endpoint is the kubernetes ingress, this is correct from the point of view of gitlab alone, but not from the outside.
If we set https here, gitlab will create redirects from http to https which in turn causes some yet unknown problems that hinder the container from working properly (maybe related to kubernetes probes). There are no such problems when using http.
But there is one caveat: now gitlab uses http as protocol for repo URLs in the web interface.
So we need to specify https as external protocol and fix any issues with container setup.

Note that specifying https also corresponds to docs: https://docs.gitlab.com/omnibus/settings/ssl/index.html#configure-https-manually