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/aidl/impl/grpc/Android.bp b/automotive/vehicle/aidl/impl/grpc/Android.bp
index fd1d1ca..7a8da59 100644
--- a/automotive/vehicle/aidl/impl/grpc/Android.bp
+++ b/automotive/vehicle/aidl/impl/grpc/Android.bp
@@ -22,7 +22,7 @@
         "aprotoc",
         "protoc-gen-grpc-cpp-plugin",
     ],
-    cmd: "$(location aprotoc) -I$$(dirname $(location proto/VehicleServer.proto)) -Ihardware/interfaces/automotive/vehicle/aidl/impl/proto -Iexternal/protobuf/src --plugin=protoc-gen-grpc=$(location protoc-gen-grpc-cpp-plugin) $(location proto/VehicleServer.proto) --grpc_out=$(genDir) --cpp_out=$(genDir)",
+    cmd: "$(location aprotoc) -I$$(dirname $(location proto/VehicleServer.proto)) -Ihardware/interfaces/automotive/vehicle/aidl/impl/proto -Iexternal/protobuf/src --plugin=protoc-gen-grpc=$(location protoc-gen-grpc-cpp-plugin) $(location proto/VehicleServer.proto) --grpc_opt=generate_mock_code=true --grpc_out=$(genDir) --cpp_out=$(genDir)",
     srcs: [
         "proto/VehicleServer.proto",
         ":libprotobuf-internal-protos",
@@ -31,6 +31,7 @@
     out: [
         "VehicleServer.pb.h",
         "VehicleServer.grpc.pb.h",
+        "VehicleServer_mock.grpc.pb.h",
     ],
     visibility: ["//visibility:private"],
 }