ot cli command is called networkkey now (#26210)

See https://github.com/openthread/openthread/blob/main/src/cli/README.md#networkkey

Author: markus-becker-tridonic-com

docs/guides/nrfconnect_examples_cli.md

@@ -83,7 +83,7 @@ available options for the given command.
 are accessible from the shell, but they must preceded by `ot`. For example:
 
 ```shell
-uart:~$ ot masterkey
+uart:~$ ot networkkey
 00112233445566778899aabbccddeeff
 Done
 ```