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

docs/admin_api/user_admin_api.md

@@ -146,6 +146,7 @@ Body parameters:
 - `admin` - **bool**, optional, defaults to `false`. Whether the user is a homeserver administrator,
   granting them access to the Admin API, among other things.
 - `deactivated` - **bool**, optional. If unspecified, deactivation state will be left unchanged.
+- `locked` - **bool**, optional. If unspecified, locked state will be left unchanged.
 
   Note: the `password` field must also be set if both of the following are true:
   - `deactivated` is set to `false` and the user was previously deactivated (you are reactivating this user)

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`