synapse: Add support for appservices and use secrets better

roles/synapse/meta/argument_specs.yaml

@@ -116,3 +116,29 @@ argument_specs:
         type: str
         required: false
         default: 16-alpine
+
+      synapse_appservices:
+        description: List of appservices to run with synapse. They will be installed in separate containers.
+        type: list
+        required: false
+        default: []
+        elements: dict
+        options:
+          id:
+            description: A unique, user-defined ID of the application service which will never change
+            type: str
+            required: true
+          host:
+            description: Hostname the appservice is accessible to synapse at
+            type: str
+            required: true
+          as_token:
+            description: A secret token that the application service will use to authenticate requests to the homeserver
+            type: str
+            required: true
+          hs_token:
+            description: A secret token that the homeserver will use authenticate requests to the application service
+            type: str
+            required: true
+      synapse_doublepuppet_token:
+        description: Double puppeting token for appservices. Required if synapse_appservices is not empty.