Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/735

Also switches to using `docker system prune -a` for a less invasive
cleanup of Docker images and related resources.

Related to #681 (Github Pull Request)

Related to #681 (Github Pull Request)

Related to #681 (Github Pull Request)

This broke in 63a49bb2dc.

Proxying the OpenID Connect endpoints is now possible,
but needs to be enabled explicitly now.

Supersedes #702 (Github Pull Request).

This patch builds up on the idea from that Pull Request,
but does things in a cleaner way.

Regression since 63a49bb2dc.

Related to #685 (Github Issue).

We now automatically expose the APIs when Synapse Admin is enabled.

The SSL certificates should be accessible to the nginx proxy container, not the synapse container.

Discussed in #669 (Github Issue).

Interestingly, no one has reported this failure before #662 (Github
Issue).

It doesn't make sense to keep saying that we support such old Ansible
versions, when we're not even testing on anything close to those.

Time is also passing and such versions are getting more and more
ancient. It's time we bumped our requirements to something that is more
likely to work.

Improved formatting for a header that was attached to the previous paragraph (...by inserting a newline).

modified example for jitsi ldap authentication to show all available variables.

Change anonymized to more proper term as server vice this is not anonymized. Server name is the first parameter that is collected. And if server happens to be for individual use these statistics would be at personal level without any anonymising.

We recently had a report of the Postgres backup container's log file
growing the size of /var/lib/docker until it ran out of disk space.

Trying to prevent similar problems in the future.

Related to #620 (Github Pull Request).

Potentially the CURLing could be a better approach, since then you don't leave spare sessions hanging.

Add an example to open all domains for registration in relation to black- and whitelists.