Implements admin API to lock an user (MSC3939) (#15870)

docs/usage/configuration/config_documentation.md

@@ -3631,6 +3631,7 @@ This option has the following sub-options:
 * `prefer_local_users`: Defines whether to prefer local users in search query results.
    If set to true, local users are more likely to appear above remote users when searching the
    user directory. Defaults to false.
+* `show_locked_users`: Defines whether to show locked users in search query results. Defaults to false.
 
 Example configuration:
 ```yaml
@@ -3638,6 +3639,7 @@ user_directory:
     enabled: false
     search_all_users: true
     prefer_local_users: true
+    show_locked_users: true
 ```
 ---
 ### `user_consent`