api docs: Correct errors in the stream creation documentation.

* Reordered the settings relevant without stream creation to the top.
* Removed useless/misleading defaults for optional parameters.
* Clarified description of the announce and authorization_errors_fatal settings.
* Clarified that `invite_only` only applies for stream creation.
  (It's annoying to do so for its friends because they are including
   common description content and OpenAPI doesn't have a way to have
   extra content in a place you included something)

Fixes #14705.

zerver/openapi/python_examples.py

@@ -62,7 +62,7 @@ def add_subscriptions(client: Client) -> None:
                                     '200_0')
 
     # {code_example|start}
-    # To subscribe another user to a stream, you may pass in
+    # To subscribe other users to a stream, you may pass
     # the `principals` argument, like so:
     user_id = 25
     result = client.add_subscriptions(