tests: net: lib: mqtt: v3_1_1: Add test variant with MQTT 5.0 enabled

Add test variant which enables MQTT 5.0 support. MQTT 3.1.1 should still
work just fine in such case, so it needs to be verified that's the case.

Signed-off-by: Robert Lubos <robert.lubos@nordicsemi.no>
4 files changed