QSQL: add support for PostgreSQL 11

Add support for PostgreSQL 11 by adding QPSQLDriver::Version11 and use
it in qMakePSQLVersion().

[ChangeLog][QSQL][PostgreSQL] Added support for PostgreSQL 11

Fixes: QTBUG-71642
Change-Id: Ie3cd3a81fd00084b587457b91b4e92c2e7001172
Reviewed-by: Andy Shaw <andy.shaw@qt.io>
Reviewed-by: Robert Szefner <robertsz27@interia.pl>

src/plugins/sqldrivers/psql/qsql_psql.cpp

@@ -1060,8 +1060,10 @@ static QPSQLDriver::Protocol qMakePSQLVersion(int vMaj, int vMin)
     }
     case 10:
         return QPSQLDriver::Version10;
+    case 11:
+        return QPSQLDriver::Version11;
     default:
-        if (vMaj > 10)
+        if (vMaj > 11)
             return QPSQLDriver::UnknownLaterVersion;
         break;
     }

src/plugins/sqldrivers/psql/qsql_psql_p.h

@@ -92,6 +92,7 @@ public:
         Version9_5 = 21,
         Version9_6 = 22,
         Version10 = 23,
+        Version11 = 24,
         UnknownLaterVersion = 100000
     };