Make Synapse quieter by default

Hopefully fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/2849

Related to:
- https://github.com/matrix-org/synapse/issues/16101
- https://github.com/matrix-org/synapse/issues/16208

roles/custom/matrix-synapse/defaults/main.yml

@@ -439,7 +439,19 @@ matrix_synapse_container_additional_volumes: []
 # This list gets populated dynamically based on Synapse extensions that have been enabled.
 # Contains definition objects like this: `{"name": "..", "level": "DEBUG"}
 matrix_synapse_additional_loggers: "{{ matrix_synapse_additional_loggers_auto + matrix_synapse_additional_loggers_custom }}"
-matrix_synapse_additional_loggers_auto: []
+
+matrix_synapse_additional_loggers_auto:
+  # By default, we're disabling some useless (and even toxic) spammy WARNING-level logs.
+  # Related to:
+  # - https://github.com/matrix-org/synapse/issues/16208
+  # - https://github.com/matrix-org/synapse/issues/16101
+  - name: synapse.http.matrixfederationclient
+    level: CRITICAL
+  - name: synapse.federation.sender.per_destination_queue
+    level: CRITICAL
+  - name: synapse.handlers.device
+    level: CRITICAL
+
 matrix_synapse_additional_loggers_custom: []
 
 # A list of appservice config files (in-container filesystem paths).