Add commitHlc as an optional field to MultiWrite{Request,Reply}

Summary:
As title, in support of read atomicity on TAO. No op, fields not currently used and is
`optional`. I also had to add it to the MSMWv2 endpoints as they go into the same `MultiWriteResult` struct (through multiple layers of abstraction) in CC.

Reviewed By: davidgoode

Differential Revision: D61860932

fbshipit-source-id: 2cb5c4efc005d405886d4ea27a31df762bdd9f65

mcrouter/lib/network/gen/Common.thrift

@@ -63,7 +63,7 @@ cpp.virtual
 )
 struct McVersionReply {
   1: carbon_result.Result result
-  2: binary (cpp.type = "folly::IOBuf") value
+  2: binary_5325 value
   3: string message
   4: i16 appSpecificErrorCode
 }(cpp.methods = "
@@ -251,3 +251,6 @@ struct GoAwayRequest {
 ",
 cpp.virtual
 )
+
+// The following were automatically generated and may benefit from renaming.
+typedef binary (cpp.type = "folly::IOBuf") binary_5325