* if variable to bind an exporter container to a host port is set, have matrix-domain.conf (nginx) support this

* manipulate some variables to account for just port numbers or 0.0.0.0 IPs

* Make sure to use the right variable in the init.yml files

* Update roles/matrix-prometheus-node-exporter/tasks/init.yml

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

* Update roles/matrix-prometheus-postgres-exporter/tasks/init.yml

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

* remove extraneous variables and whitespace

Co-authored-by: Luca Bilke <luca@gmail.com>
Co-authored-by: Slavi Pantaleev <slavi@devture.com>

Related to https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/1939

Basic system stats, to show stuff the synapse metrics
can't show such as resource usage by bridges, etc

Seems to work fine as well.

This too has only been tested on debian amd64 so far