* one var to control encryption across all bridges

* move var to matrix-base

Related to https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/2427

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.

"Community" support

- has been removed from mautrix/facebook in v0.3.3:
  31cac6fb5e

- has been removed from mautrix/signal in v0.2.2:
  1f27a608a6

- will be removed in the next mautrix/instagram release:
  e2ae1ca503

- will be removed in the next mautrix/twitter release:
  3893075265

Updates based off the variable names used in mautrix-facebook role.

Also update port number in defauts/main.yml, and disable presence
checking, because Twitter doesn't support that.

Source: 12f420ab95/mautrix_twitter/example-config.yaml

find roles/matrix-bridge-mautrix-twitter -type f -exec sed -i \
  -e 's/facebook/twitter/g' \
  -e 's/Facebook/Twitter/g' \
  -e 's/FB/Twitter/g' \
  -e 's/fb/twitter/g' {} +

Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/806

I had intentionally held it back in 39ea3496a4
until:
- it received more testing (there were a few bugs during the
migration, but now it seems OK)
- this migration guide was written

If a service is enabled, a database for it is created in postgres with a uniqque password. The service can then use this database for data storage instead of relying on sqlite.

This also disables presence if it's disabled for Synapse.

Related to #193, but for the Facebook bridge.
(other bridges can be changed to do the same later).

This patch makes the bridge configuration entirely managed by the
Ansible playbook. The bridge's `config.yaml` and `registration.yaml`
configuration files are regenerated every time the playbook runs.

This allows us to apply updates to those files and to avoid
people having to manage the configuration files manually on the server.

-------------------------------------------------------------

A deficiency of the current approach to dumping YAML configuration in
`config.yaml` is that we strip all comments from it.
Later on, when the bridge actually starts, it will load and redump
(this time with comments), which will make the `config.yaml` file
change.

Subsequent playbook runs will report "changed" for the
"Ensure mautrix-facebook config.yaml installed" task, which is a little
strange.

We might wish to improve this in the future, if possible.

Still, it's better to have a (usually) somewhat meaningless "changed"
task than to what we had -- never rebuilding the configuration.