Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/1023

Related to https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/1009

Potentially fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/1022

**HSTS Preloading:**
In its strongest and recommended form, the [HSTS policy](https://www.chromium.org/hsts) includes all subdomains, and indicates a willingness to be “preloaded” into browsers:
`Strict-Transport-Security: max-age=31536000; includeSubDomains; preload`

**X-Xss-Protection:**
`1; mode=block` which tells the browser to block the response if it detects an attack rather than sanitising the script.

More Production ready nginx headers for Matrix client element.

Related to https://github.com/Awesome-Technologies/synapse-admin/issues/132

GoMatrixHosting v0.4.3

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

It's an optional service, so we shouldn't bother most people with it.

Update mautrix-facebook docs

Upgrade synapse-admin (0.7.0 -> 0.7.2)

This reverts commit f825c7c263.

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

Switch to official coturn image

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.

security** node-exporter data & port publicly exposed

This reverts commit d0cd709c08.

Don't expose nginx version with each response

updated matrix_grafana_docker_image to v7.5.4

Improve security for grafana

Fix prometheus network for ansible < 2.8

This reverts commit 68ca81c8c2.

- duplicate X-Content-Type-Options
- X-Frame-Options header
- Referrer-Policy [Might consider adding variable]
- Secure flag with cookies
- matrix_grafana_content_security_policy variable for [Content Security Policy](https://grafana.com/docs/grafana/latest/administration/configuration/#content_security_policy)

Latest stable grafana version is [7.5.4 (2021-04-14)](https://github.com/grafana/grafana/releases/tag/v7.5.4)

Supposedly fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/907

Update prometheus node exporter (1.1.0->1.1.2)

Update prometheus (2.24.1->2.26.0)