Add subscribe to VHAL proto.

The latest IVehicleHardware adds Subscribe/Unsubscribe function
to replace the existing updateSampleRate. This CL adds the
Subscribe function to protobuf definition and implements it.

Test: atest GRPCVehicleHardwareUnitTest GRPCVehicleProxyServerUnitTest
Flag: EXEMPT hal change
Bug: 328316981
Merged-In: I4f02885b77f21a215a8b282be583f76118e400ba
(cherry-picked from commit: f1a869055fcd6ea980e329e86d71ace715427d30)

Change-Id: I4f02885b77f21a215a8b282be583f76118e400ba
diff --git a/automotive/vehicle/TEST_MAPPING b/automotive/vehicle/TEST_MAPPING
index e1a90cb..117c872 100644
--- a/automotive/vehicle/TEST_MAPPING
+++ b/automotive/vehicle/TEST_MAPPING
@@ -55,5 +55,10 @@
     {
       "name": "VehicleHalProtoMessageConverterTest"
     }
+  ],
+  "postsubmit": [
+    {
+      "name": "VehicleHalProtoMessageConverterTest"
+    }
   ]
 }