[mqtt.homeassistant] Stable jsondb discovery result (#13401)

[mqtt.homeassistant] Stable jsondb discovery result (#13401)

* [mqtt.homeassistant] Stable jsondb serialization for discovery results

Similar to openhab/openhab-core#2436, we want
to have consistent ordering of data in JSONDB. This is fixing the jsondb
order for mqtt.homeassistant discovery results, specifically, the
"topics" property.

* [mqtt.homeassistant] order using full topic string, not by subcomponent

Signed-off-by: Sami Salonen <ssalonen@gmail.com>