This change should make it more obvious which order the steps must be done

Also indicates that the Mautrix googlechat bridge is a replacement for hangouts.

Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/1322

Related to https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/1282

It's mostly due to Docker CE dropping its repositories (and support) for
Debian 9.
If one installs Docker manually (likely a package named `docker.io`), it
will likely still work.
In any case, Debian 9 is old and end-of-life now, so advertising support
for it is not productive.

Ubuntu ended support for 16.04 in April

This avoids having to create a new room and to click the "Add widgets, bridges & bots" link (Formerly the four-squares-icon)

matrix_jitsi_jicofo_component_secret var removed #1139

Related to https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/1242

Improvement of documentation

Co-authored-by: Jan <31133207+Jaffex@users.noreply.github.com>

Document how to enable relay functionality in a room

Co-authored-by: Jan <31133207+Jaffex@users.noreply.github.com>

The default of using the `matrix` database is better anyway.

The attached code for the "Serving the Federation API with your certificates and matrix-nginx-proxy" section suggests using the matrix.<your-domain> certificate for the federation API as opposed to the necessary <your-domain> certificate for the federation to work. This can cause some confusion to readers.