upgrade to 5.5 (#9798)

* upgrade to 5.5

* add 5.6 upgrade db

model/version.go

@@ -13,6 +13,7 @@ import (
 // It should be maintained in chronological order with most current
 // release at the front of the list.
 var versions = []string{
+	"5.5.0",
 	"5.4.0",
 	"5.3.0",
 	"5.2.0",