Add support for a prometheus postgres exporter

Update IRC channel

This commit introduces a new role that downloads and installs the
prometheus community postgres exporter  https://github.com/prometheus-community/postgres_exporter.
A new credential is added to matrix_postgres_additional_databases that
allows the exporter access to the database to gather statistics.
A new dashboard was added to the grafana role, with some refactoring
to enable the dashboard only if the new role is enabled.
I've included some basic instructions for how to enable the role in
the Docs section.

In terms of testing, I've tested enabling the role, and disabling
it to make sure it cleans up the container and systemd role.

Check IRC appservice service is present before stopping it

Server migration doc update

Annotate server migration with a note in regard to migration between different architectures and the need to dump/restore the database.

Update PostgreSQL Maintenance page

Added a mid-sized VPS configuration with configuration changes to the PostgreSQL database config.

Deleted single quotes in one of the examples to unify the examples

Update IRC appservice

Synapse LDAP auth: add support for Active Directory

Mjolnir antispam

Updated nginx-proxy (1.20.0 -> 1.21.0)

GoMatrixHosting v0.4.7

Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/1084

Conversation: https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/1083#discussion_r638671860

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

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

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

HSTS preload + X-XSS enables

OCSP Stapling SSL manually-managed

# chain.pem file is required for 'ssl_trusted_certificate`

Allow Jitsi XMPP websocket support for users using own webserver.

Remove synapse-admin incompatibility note

I changed the conditional statement in prosody systemd template to bind the localhost port by default if people have set ```matrix_nginx_proxy_enabled == false ```.
Hopefully that should make it the default behaviour now.

Fix hydrogen

Added:
 - Conditional localhost Port bindings for Jitsi Prosody systemd template
- Added variable to main.yml to allow overriding from vars.yml