If someone is using Dendrite and enabling Grafana, we'll no longer
download Synapse dashboards.

If someone is not using node-exporter, we'll no longer download node
exporter dashboards.

Related to https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/2133

* 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>

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.

This reverts commit d0cd709c08.

Signed-off-by: Ahmad Haghighi <haghighi@fedoraproject.org>

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