Stop using deprecated (in Synapse v1.59) user_dir and appservice workers

Source: https://github.com/matrix-org/synapse/blob/v1.59.0/docs/upgrade.md#deprecation-of-the-synapseappappservice-and-synapseappuser_dir-worker-application-types

As an alternative, we should probably find a way to run one or a few
more generic workers (which will handle appservice and user_dir stuff) and
update `homeserver.yaml` so that it would point to the name of these workers using
`notify_appservices_from_worker` and `update_user_directory_from_worker` options.

For now, this solves the deprecation, so we can have a peace of mind
going forward.

We're force-setting these worker counts to 0, so that we can clean up
existing homeservers which use these worker types. In the future, these
options will either be removed or repurposed (so that they transparently
create more generic workers that handle user_dir/appservice loads).

roles/matrix-synapse/tasks/validate_config.yml

@@ -12,13 +12,24 @@
     - "matrix_synapse_database_password"
     - "matrix_synapse_database_database"
 
+- name: Fail if asking to configure deprecaed workers (appservice, userdir)
+  fail:
+    msg: >-
+      `{{ item }}` cannot be more than 0.
+      This type of worker has been deprecated since Synapse v1.59.
+      Please remove your `{{ item }}` configuration to solve this problem.
+      See: https://github.com/matrix-org/synapse/blob/v1.59.0/docs/upgrade.md#deprecation-of-the-synapseappappservice-and-synapseappuser_dir-worker-application-types
+  when: "vars[item]|int != 0"
+  with_items:
+    - "matrix_synapse_workers_appservice_workers_count"
+    - "matrix_synapse_workers_user_dir_workers_count"
+
 - name: Fail if asking for more than 1 instance of single-instance workers
   fail:
     msg: >-
       `{{ item }}` cannot be more than 1. This is a single-instance worker.
   when: "vars[item]|int > 1"
   with_items:
-    - "matrix_synapse_workers_appservice_workers_count"
     - "matrix_synapse_workers_pusher_workers_count"
     - "matrix_synapse_workers_federation_sender_workers_count"