DOCS-14079 add audit event for logout

Author: jmd-mongo

source/reference/audit-message.txt

@@ -656,6 +656,36 @@ associated ``param`` details and the ``result`` values, if any.
 
 
      - ``0`` - Success
+   
+   * - :authaction:`logout`
+
+     - .. code-block:: none
+          :copyable: false
+
+          {
+            reason: <string>,
+            initialUsers: [ <document>, ... ],
+            updatedUsers: [ <document>, ... ], 
+          }
+
+       ``reason`` will be either:
+         - "Explicit logout from <database>"
+         - "Implicit logout due to client connection closure"
+
+       ``initialUsers`` is an array of documents containing users 
+       authenticated on the current client prior to logout.
+
+       ``updatedUsers`` is an array of documents containing users 
+       expected to be authenticated on the current client after the 
+       logout event. 
+
+       Each document in ``initialUsers`` and ``updatedUsers`` contains:
+         - ``user``: the username
+         - ``db``: the database ``user`` is authenticated to
+
+       .. versionadded:: 5.0
+
+     - ``0`` - Success
 
 
 .. [#performance]