[3.11] pythongh-104711: Add security warning to the CGIHTTPRequestHandler document (pythonGH-115915)

(cherry picked from commit dac8ff4)

Co-authored-by: AN Long <[email protected]>

Author: aisk

Doc/library/http.server.rst

@@ -502,6 +502,12 @@ the ``--cgi`` option::
 
         python -m http.server --cgi
 
+.. warning::
+
+   :class:`CGIHTTPRequestHandler` and the ``--cgi`` command line option
+   are not intended for use by untrusted clients and may be vulnerable
+   to exploitation. Always use within a secure environment.
+
 .. _http.server-security:
 
 Security Considerations