[AAP-64338] Enhance documentation for gateway_api.py (#118)

* Enhance documentation for gateway_api.py

Updated documentation to clarify plugin usage and warnings.

* Update gateway_api.py

* Enhance API description with usage link

Added a reference link for API usage in the description.

* Update gateway_api.py

Author: nickbhasin

plugins/lookup/gateway_api.py

@@ -13,6 +13,9 @@
 description:
   - Returns GET requests from the Automation Platform Gateway API. See
     U(https://docs.ansible.com/TODO) for API usage.
+  - This plugin is designed to support Gateway API endpoints used to manage resources with ansible.platform modules,
+    such as users, teams, organizations, settings, role_definitions, and related endpoints.
+  - Querying APIs outside of the Gateway API (such as Automation Hub, Galaxy etc.) is not supported and may lead to unexpected errors.
 options:
   _terms:
     description: