The old variables existed as well, but I inteded to use these new ones.

The user may be running Prometheus elsewhere. It doesn't need to be
getting installed using the current playbook.

Regression since ce2f541deb

This requires at least `v0.14.0-2` of the `prometheus-postgres-exporter`
Ansible role.

This requires at least `v1.7.0-2` of the `prometheus-node-exporter`
Ansible role.

This is an attempt at optimizing service startup.

The effect is most pronounced when many services are restarted one by one.
The systemd service manager role sometimes does this - for example when `just install-service synapse` runs.
In such cases, a 5-second delay for each Synapse worker service
(or other bridge/bot service that waits on the homeserver) quickly adds up to a lot.

When services are all stopped fully and then started, the effect is not so pronounced, because
`matrix-synapse.service` starts first and pulls all worker services (defined as `Wants=` for it).
Later on, when the systemd service manager role "starts" these worker services, they're started already.
Even if they had a 5-second wait each, it would have happened in parallel.

Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/3090

Related to https://github.com/mautrix/signal/issues/422

`--mount` is safer, as `-v` has the side-effect of creating the "source"
destination as a directory if it doesn't exist yet.
We don't need such magic.

Related to e5130372b9.

Depending on the `options` that people provide, this may break
compatibility.

Depending on the `options` that people provide, this may break
compatibility.

Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/3088

Looks like the migration to the Go-based Signal bridge hardcoded the
`signalbot` username instead of using the variable we had.
Related to: https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/3041

Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/3089

This is mostly so as to avoid referring to variables from other roles,
like `matrix_nginx_proxy_proxy_matrix_client_api_addr_with_container`.

This should come (and already does) from group_vars/matrix_servers

This also makes it handle the `/_matrix/client/v3/register` endpoint,
not just `/_matrix/client/r0/register`

This reverts commit bf95ad2235.

This was a bad idea.
It's better to have people manually define the password.

Otherwise, `matrix_homeserver_generic_secret_key` changing some day in
the future would break the bot and one would have to figure out how to
reset its password manually.

Using an explicit password is more stable.