Related to https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/2427
`metrics_enabled` should only expose the metrics locally, on the
container network, so that a local Prometheus can consume them.
Exposing them publicly should be done via a separate toggle (`metrics_proxying_enabled`).
This is how all other roles work, so this makes these mautrix roles consistent with the rest.
* Allow the mautrix whatsapp relaybot to be enable with a variable
This allows a user to enable the relaybot by setting a variable in
`vars.yml` in the same way that the mautrix signal relaybot is
configured.
* Correct default values for mautrix whatsapp relaybot variables
* Add documentation for using the relaybot with mautrix whatsapp
* Adjust variable names to better reflect what they do
* Set default variables properly and use to_json in template
