Since upgrading mautrix-signal (v0.6.3 -> v0.7.0) in 76fec0b8632804194ae54dce3328fef2b6e6b3c2,
we expect double-puppeting to require the new appservice double-puppeting method.

This commit switches the mautrix-signal bridge to it.

Related to:
- https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/3479
- https://github.com/mautrix/signal/releases/tag/v0.7.0
- https://mau.fi/blog/2024-08-mautrix-release/

It seems like the new version does not support a `/metrics` endpoint.
We skip keep the Ansible variables, but they're not doing anything.

Closes https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/3481

This paves the way for installing other roles into `roles/galaxy` using `ansible-galaxy`,
similar to how it's done in:

- https://github.com/spantaleev/gitea-docker-ansible-deploy
- https://github.com/spantaleev/nextcloud-docker-ansible-deploy

In the near future, we'll be removing a lot of the shared role code from here
and using upstream roles for it. Some of the core `matrix-*` roles have
already been extracted out into other reusable roles:

- https://github.com/devture/com.devture.ansible.role.postgres
- https://github.com/devture/com.devture.ansible.role.systemd_docker_base
- https://github.com/devture/com.devture.ansible.role.timesync
- https://github.com/devture/com.devture.ansible.role.vars_preserver
- https://github.com/devture/com.devture.ansible.role.playbook_runtime_messages
- https://github.com/devture/com.devture.ansible.role.playbook_help

We just need to migrate to those.

Not doing {% if matrix_admin %} checks in the YAML also fixes some issues
with indentation being incorrect sometimes.

This should be backward compatible, except for mautrix-signal's case
where `matrix_mautrix_signal_bridge_permissions` previously existed
as a string, not a dictionary. `tasks/validate_config.yml` will catch
the problem an even provide a quick fix.

Related to https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/1939

While it's kind of nice having it, it's also somewhat raw
and unnecessary.

Having a good default and not even mentioning it seems better
for most users.

People who need a more exposed bridge (rare) can use
override the default configuration using
`matrix_mautrix_signal_configuration_extension_yaml`.