Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/1073

Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/1047

This reverts commit 1fb54a37cb.

Seems like it's been pulled or something. It used to exist, but not
anymore. Not sure what's going on.

Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/1017

Related to
https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/1010

Related to https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/1010

This reverts commit f825c7c263.

Related to https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/1010

Expected to have regressed after https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/1008

This patch comes with its own downsides (as described in the comments
for matrix_prometheus_node_exporter_container_http_host_bind_port),
but at least there's:
- no security issue
- metrics remain readable from matrix-prometheus (even if the network metrics are inaccurate)

A better patch is certainly welcome.

Not sure why this had been done in the first place.
It doesn't make any sense.

There's no relation between matrix-nginx-proxy and
prometheus-node-exporter.

This was causing a port conflict when `matrix_nginx_proxy_enabled: false`.

Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/983

Related to https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/868

Some people have reported Dimension failing to contact
matrix-nginx-proxy/Synapse on startup. This attempts to
delay Dimension startup some more.

Related to https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/966

That is:
- enabled in the role by default
- disabled in the compilation (playbook), if considered an optional
component

We don't point them straight to Synapse anymore, but rather
to matrix-nginx-proxy, which forwards to Synapse (or something else).

This variable was previously undefined in the role and was only getting
defined via `group_vars/matrix_servers`.

We now properly initialize it (and its good default value) in the role
itself.

Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/683

- add matrix_postgres_backup_databases to be build on top of matrix_postgres_additional_databases
- POSTGRES_DB is now directly set from matrix_postgres_backup_databases while building the templates/env-postgres-backup.j2

- adjusted env-postgres-backup.j2 to use the new role specific variables

Mostly affects people who disable the integrated `matrix-nginx-proxy`.

Related to https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/456
and more specifically 4d62a75f6f.

People who were disabling matrix-nginx-proxy (in favor of their own
nginx webserver) and also overriding `matrix_federation_public_port`,
found that the generated nginx configuration still hardcoded `8448`,
which forced their nginx server to use that, regardless of the fact
that `matrix_federation_public_port` was pointing elsewhere.

We now allow for the in-container federation port to be configurable,
and also automatically wire things properly.

Related to: https://matrix.org/blog/2021/02/18/synapse-1-27-0-released#dropping-armv7-docker-images

The official Etherpad Docker image has no support for sqlite3 databases.

don't bind to any host port if nginx_proxy is used
only bind to localhost if it's not used

.. and other documentation improvements.