Update C++ SDK version to 12.0.0.

Author: jonsimantov

cpp_sdk_version.json

@@ -1,5 +1,5 @@
 {
-  "released": "11.10.0",
-  "stable": "11.10.0",
-  "head": "11.10.0"
+  "released": "12.0.0",
+  "stable": "12.0.0",
+  "head": "12.0.0"
 }