feat(autoware_adapi_v1_msgs): rename mrm request sender (#91)

Signed-off-by: Takagi, Isamu <isamu.takagi@tier4.jp>

Author: isamu-takagi

autoware_adapi_v1_msgs/system/msg/MrmRequest.msg

@@ -2,5 +2,5 @@ uint16 UNKNOWN = 0
 uint16 CANCEL = 1    # Cancel the MRM request.
 uint16 DELEGATE = 2  # Delegate the selection of MRM behavior to Autoware.
 
+string sender        # The identifier of the request sender.
 uint16 strategy
-string user      # The identifier of the request sender.