introduce firstHlc in HlcTracker

Summary:
introduce firstHlc in HlcTracker. Ensure it is persisted on warm rolls and correctly updated through shard lifecycle changes:
1. shard subscription
2. shard dataloss
3. shard resubscription

The firstHlc will be used later in the stack (see D64814926) to identify items in cache that are not covered by the currently active wh subscription.
For more details, see: https://fburl.com/gdoc/3izqv6ei

Differential Revision: D64706643

fbshipit-source-id: 660d6bb6ffbb21a7c727f8590f63e74588eccd3d

mcrouter/lib/network/gen/Common.thrift

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