Related to https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/3442

* Created role for synapse-usage-exporter

* Apply suggestions from code review

Co-authored-by: Slavi Pantaleev <slavi@devture.com>

* Renaming docker variables and moving synapse stats config location

* Respect devture_systemd_docker_base_docker_service_name

---------

Co-authored-by: Slavi Pantaleev <slavi@devture.com>