[BREAKING] [proto] Use google/protobuf/empty.proto (#131)

#### Type of change

- Improvement (improvement to code, performance, etc)
- Breaking change
 
#### Description

- Use `google/protobuf/empty.proto`

#### Related issues

- resolves #130

Signed-off-by: Liran Funaro <[email protected]>

Author: liran-funaro

api/protocoordinatorservice/coordinator.pb.go

@@ -11,15 +11,16 @@ option go_package = "github.com/hyperledger/fabric-x-committer/api/protocoordina
 package protocoordinatorservice;
 
 import "api/protoblocktx/block_tx.proto";
+import "google/protobuf/empty.proto";
 
 service Coordinator {
     rpc BlockProcessing(stream Batch) returns (stream protoblocktx.TransactionsStatus);
-    rpc SetLastCommittedBlockNumber (protoblocktx.BlockInfo) returns (Empty) {};
-    rpc GetLastCommittedBlockNumber (Empty) returns (protoblocktx.LastCommittedBlock) {};
-    rpc GetNextExpectedBlockNumber (Empty) returns (protoblocktx.BlockInfo) {};
+    rpc SetLastCommittedBlockNumber (protoblocktx.BlockInfo) returns (google.protobuf.Empty) {};
+    rpc GetLastCommittedBlockNumber (google.protobuf.Empty) returns (protoblocktx.LastCommittedBlock) {};
+    rpc GetNextExpectedBlockNumber (google.protobuf.Empty) returns (protoblocktx.BlockInfo) {};
     rpc GetTransactionsStatus(protoblocktx.QueryStatus) returns (protoblocktx.TransactionsStatus);
-    rpc GetConfigTransaction(Empty) returns (protoblocktx.ConfigTransaction) {};
-    rpc NumberOfWaitingTransactionsForStatus(Empty) returns (WaitingTransactions);
+    rpc GetConfigTransaction(google.protobuf.Empty) returns (protoblocktx.ConfigTransaction) {};
+    rpc NumberOfWaitingTransactionsForStatus(google.protobuf.Empty) returns (WaitingTransactions);
 }
 
 // A committer's representation of a block in the blockchain.
@@ -49,6 +50,3 @@ message TxRef {
 message WaitingTransactions {
     int32 count = 1;
 }
-
-message Empty {
-}