Add idempotency_key to CallEntryMessage & OneWayCallEntryMessage.

dev/restate/service/protocol.proto

@@ -25,6 +25,7 @@ enum ServiceProtocolVersion {
   // Added
   // * New entry to cancel invocations: CancelInvocationEntryMessage
   // * New entry to retrieve the invocation id: GetCallInvocationIdEntryMessage
+  // * New field to set idempotency key for Call entries
   V3 = 3;
 }
 
@@ -317,6 +318,8 @@ message CallEntryMessage {
   // If this invocation has a key associated (e.g. for objects and workflows), then this key is filled in. Empty otherwise.
   string key = 5;
 
+  string idempotency_key = 6;
+
   oneof result {
     bytes value = 14;
     Failure failure = 15;
@@ -346,6 +349,8 @@ message OneWayCallEntryMessage {
   // If this invocation has a key associated (e.g. for objects and workflows), then this key is filled in. Empty otherwise.
   string key = 6;
 
+  string idempotency_key = 7;
+
   // Entry name
   string name = 12;
 }