Make bridge permissions more easily configurable

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.

roles/matrix-bridge-mautrix-signal/templates/config.yaml.j2

@@ -223,8 +223,7 @@ bridge:
     #        * - All Matrix users
     #   domain - All users on that homeserver
     #     mxid - Specific user
-    permissions:
-        {{ matrix_mautrix_signal_bridge_permissions|from_yaml }}
+    permissions: {{ matrix_mautrix_signal_bridge_permissions|to_json }}
 
     relay:
         # Whether or not relay mode should be allowed. If allowed, `!signal set-relay` can be used to turn any