Fix usage of add_uaa_key command

Switch is --pem-file, not --pem_file.

(cherry picked from commit 4a2f61a)

Author: acogoluegnes

deps/rabbitmq_auth_backend_oauth2/src/Elixir.RabbitMQ.CLI.Ctl.Commands.AddUaaKeyCommand.erl

@@ -27,7 +27,7 @@
 
 
 usage() ->
-    <<"add_uaa_key <name> [--json=<json_key>] [--pem=<public_key>] [--pem_file=<pem_file>]">>.
+    <<"add_uaa_key <name> [--json=<json_key>] [--pem=<public_key>] [--pem-file=<pem_file>]">>.
 
 switches() ->
     [{json, string},