Add user_types config settings to schema and auto-generate documentation

docs/usage/configuration/config_documentation.md

@@ -764,22 +764,23 @@ max_event_delay_duration: 24h
 ---
 ### `user_types`
 
-Configuration settings related to the user types feature.
+*(object)* Configuration settings related to the user types feature. Defaults to `{}`.
 
 This setting has the following sub-options:
-* `default_user_type`: The default user type to use for registering new users when no value has been specified.
-  Defaults to none.
-* `extra_user_types`: Array of additional user types to allow. These are treated as real users. Defaults to [].
+
+* `default_user_type` (string|null): The default user type to use for registering new users when no value has been specified. Defaults to `null`.
+
+* `extra_user_types` (array): Additional user types to allow. These are treated as real users. Defaults to `[]`.
 
 Example configuration:
 ```yaml
 user_types:
-    default_user_type: "custom"
-    extra_user_types:
-      - "custom"
-      - "custom2"
+  default_user_type: custom
+  extra_user_types:
+  - custom
+  - custom2
 ```
-
+---
 ## Homeserver blocking
 
 Useful options for Synapse admins.

schema/synapse-config.schema.yaml

@@ -912,6 +912,28 @@ properties:
     default: null
     examples:
       - 24h
+  user_types:
+    type: object
+    description: >-
+      Configuration settings related to the user types feature.
+    properties:
+      default_user_type:
+        type: ["string", "null"]
+        description: >-
+          The default user type to use for registering new users when no value has been specified.
+        default: null
+      extra_user_types:
+        type: array
+        description: Additional user types to allow. These are treated as real users.
+        default: []
+        items:
+          type: string
+    default: {}
+    examples:
+      - default_user_type: custom
+        extra_user_types:
+          - custom
+          - custom2
   admin_contact:
     type: ["string", "null"]
     description: How to reach the server admin, used in `ResourceLimitError`.