Related to https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/1024

Related to https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/1061
and https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/1057

Related to https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/1057

Not sure if this is beneficial though.

Related to https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/1057

Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/1058

We may try to capture such calls and return a friendlier response (HTML
or JSON) saying "The Synapse Admin API is not enabled", but that may not
be desirable.

For now, we stick to what "upstream" recommends: "simply
don't proxy these APIs", which should lead to the same kind of 404 that
we have now.
See here: 6660912226/docs/reverse_proxy.md (synapse-administration-endpoints)

Jitsi-meet enabled websockets by default, claiming better reliability.
Matrix-nginx-proxy configuration has been set up according to the
Prosody documentation: https://prosody.im/doc/websocket

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.

- 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)

X-XSS-Protection: 1; mode=block; header, for basic XSS protection in legacy browsers.
X-Content-Type-Options: nosniff header, to disable MIME sniffing

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

This variable was previously undefined in the role and was only getting
defined via `group_vars/matrix_servers`.

We now properly initialize it (and its good default value) in the role
itself.

Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/683

Self-checks against the .well-known URIs look for the HTTP header
"Access-Control-Allow-Origin" indicating that the remode endpoint
supports CORS. But the remote server is not required to include
said header in the response if the HTTP request does not include
the "Origin" header. This is in accordance with the specification
[1] stating: 'A CORS request is an HTTP request that includes an
"Origin" header.'

This is in fact true for Gitlab pages hosting and that's why the
issue was identified.

Let's specify "Origin" header in the respective uri tasks performing
the HTTP request and ensure a CORS request.

[1] https://fetch.spec.whatwg.org/#http-requests

We have a flow like this:
1. matrix.DOMAIN vhost (matrix-domain.conf)
2. matrix-synapse vhost (matrix-synapse.conf); or matrix-corporal container, if enabled
3. (optional) matrix-synapse vhost (matrix-synapse.conf), if matrix-corporal enabled
4. matrix-synapse container

We are setting `X-Forwarded-For` correctly in step #1, but were
overwriting it in step #2 with something inaccurate.

Not doing anything in step #2 is better than doing the wrong thing.
It's probably best if we append another reverse-proxy address there
though, although what we're doing now (with this patch) seems to yield
the correct result (when matrix-corporal is not enabled).

When matrix-corporal is enabled, we still seem to do the wrong thing for
some reason. It's something to be fixed later on.

This is something that got lost during
https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/456
and more specifically 4d62a75f6f.

Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/914