adds feature to try to auto determine network_os (#18674)

This updates the network_cli connection plugin to attempt to automatically
determine the remote device os.  The device network os discovery can
be overridden by setting the ansible_network_os value.

lib/ansible/plugins/terminal/ios.py

@@ -80,3 +80,9 @@ class TerminalModule(TerminalBase):
             self._exec_cli_command('disable')
 
 
+    @staticmethod
+    def guess_network_os(conn):
+        stdin, stdout, stderr = conn.exec_command('show version')
+        if 'Cisco IOS Software' in stdout.read():
+            return 'ios'
+