Add matrix-user-creator role - automatic user account creation support

We no longer ask users to create Matrix user accounts for these bots:

- Postmoogle
- Honoroit
- Reminder Bot

Other bots and services (matrix-registration-bot, maubot, mjolnir,
Dimension, etc.) require an Access Token to run (not a password),
so this new role doesn't help for them.

It does help for the above bots though, and for defining your own
"initial user accounts" in the `matrix_user_creator_users_additional`
variable.

group_vars/matrix_servers

@@ -2677,3 +2677,37 @@ matrix_conduit_systemd_required_services_list: |
 # /matrix-conduit
 #
 ######################################################################
+
+
+######################################################################
+#
+# matrix-user-creator
+#
+######################################################################
+
+matrix_user_creator_users_auto: |
+  {{
+    [{
+      'username': matrix_bot_matrix_reminder_bot_matrix_user_id_localpart,
+      'initial_password': matrix_bot_matrix_reminder_bot_matrix_user_password,
+      'initial_type': 'bot',
+    }] if matrix_bot_matrix_reminder_bot_enabled else []
+    +
+    [{
+      'username': matrix_bot_honoroit_login,
+      'initial_password': matrix_bot_honoroit_password,
+      'initial_type': 'bot',
+    }] if matrix_bot_honoroit_enabled else []
+    +
+    [{
+      'username': matrix_bot_postmoogle_login,
+      'initial_password': matrix_bot_postmoogle_password,
+      'initial_type': 'bot',
+    }] if matrix_bot_postmoogle_enabled else []
+  }}
+
+######################################################################
+#
+# /matrix-user-creator
+#
+######################################################################