utf8mb4 encoding (#7959)

* use utf8mb4 character set for connections to mysql

* use utf8mb4 character set for tables, shorten varchar fields used in unique indexes

* migration type to update table character set

* update table character sets

* set charset for temp_user.status

* gofmt

pkg/services/sqlstore/sqlstore.go

@@ -114,7 +114,7 @@ func getEngine() (*xorm.Engine, error) {
 			protocol = "unix"
 		}
 
-		cnnstr = fmt.Sprintf("%s:%s@%s(%s)/%s?charset=utf8",
+		cnnstr = fmt.Sprintf("%s:%s@%s(%s)/%s?charset=utf8mb4",
 			DbCfg.User, DbCfg.Pwd, protocol, DbCfg.Host, DbCfg.Name)
 
 		if DbCfg.SslMode == "true" || DbCfg.SslMode == "skip-verify" {