* add prometheus-nginxlog-exporter role

* Rename matrix_prometheus_nginxlog_exporter_container_url to matrix_prometheus_nginxlog_exporter_container_hostname

* avoid referencing variables from other roles, handover info using group_vars/matrix_servers

* fix: stop service when uninstalling

fix: typo

move available arch's into a var

fix: text

* fix: prometheus enabled condition

Co-authored-by: ikkemaniac <ikkemaniac@localhost>

- forego removing Docker images - it's not effective anyway, because it
  only removes the last version.. which is a drop in the bucket, usually

- do not reload systemd - it's none of our business. `--tags=start`,
  etc., handle this

- combine all uninstall tasks under a single block, which only runs if
  we detect traces (a leftover systemd .service file) of the component.
  If no such .service is detected, we skip them all. This may lead to
  incorect cleanup in rare cases, but is good enough for the most part.

Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/2090