VOL-771 OLT heartbeat
additional GRPC endpoint for heartbeat that answers with a connection signature to detect OLT reboot /drivers restart

Change-Id: Ib4eb0f162519701c0535ca53f0875f0f83dcb833
diff --git a/protos/openolt.proto b/protos/openolt.proto
index 0dc175b..a7915c8 100644
--- a/protos/openolt.proto
+++ b/protos/openolt.proto
@@ -46,6 +46,13 @@
         };
     }
 
+    rpc HeartbeatCheck(Empty) returns (Heartbeat) {
+        option (google.api.http) = {
+          post: "/v1/HeartbeatCheck"
+          body: "*"
+        };
+    }
+
     rpc EnableIndication(Empty) returns (stream Indication) {}
 }
 
@@ -102,6 +109,10 @@
     bytes pkt = 4;
 }
 
+message Heartbeat {
+    fixed32 heartbeat_signature = 1;
+}
+
 message Onu {
     fixed32 intf_id = 1;
     fixed32 onu_id = 2;