Update HISTORY.md and version.h 6.23 release (#8552)

Summary: Pull Request resolved: https://github.com/facebook/rocksdb/pull/8552

Reviewed By: ajkr

Differential Revision: D29746828

Pulled By: jay-zhuang

fbshipit-source-id: 17d564895ae9cb675d455e73626b9a6717db6279

HISTORY.md

@@ -1,5 +1,5 @@
 # Rocksdb Change Log
-## Unreleased
+## 6.23.0 (2021-07-16)
 ### Behavior Changes
 * Obsolete keys in the bottommost level that were preserved for a snapshot will now be cleaned upon snapshot release in all cases. This form of compaction (snapshot release triggered compaction) previously had an artificial limitation that multiple tombstones needed to be present.
 

include/rocksdb/version.h

@@ -10,7 +10,7 @@
 #include "rocksdb/rocksdb_namespace.h"
 
 #define ROCKSDB_MAJOR 6
-#define ROCKSDB_MINOR 22
+#define ROCKSDB_MINOR 23
 #define ROCKSDB_PATCH 0
 
 // Do not use these. We made the mistake of declaring macros starting with