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.

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

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

# chain.pem file is required for 'ssl_trusted_certificate`

Related to https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/1055

Related to https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/1055

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

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.

This reverts commit f825c7c263.

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

Related to https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/868

Related to https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/962

Also removes some duplicate table of contents entries in maintenance-synapse.md