feat: allow using a local RSA key for machine keys (#7671)

* Allow using a local RSA key for machine keys

* Add check for key validity

* Fix naming error

* docs: provide translations of invalid key

---------

Co-authored-by: Livio Spring <livio.a@gmail.com>

internal/api/grpc/management/user_converter.go

@@ -237,6 +237,7 @@ func AddMachineKeyRequestToCommand(req *mgmt_pb.AddMachineKeyRequest, resourceOw
 		},
 		ExpirationDate: expDate,
 		Type:           authn.KeyTypeToDomain(req.Type),
+		PublicKey:      req.PublicKey,
 	}
 }