[SYS][BREAKING] Optim json size for SYStoMQTT and BTtoMQTT

[1technophile]

Description:

Breaking changes of MQTT API:
{"ohdiscovery":true}
to
{"ohdisc":true}

{"presenceTopic":"presence/"}
to
{"prestopic":"presence/"}

{"presenceUseBeaconUuid":true}
to
{"presuseuuid":true}'

{"pubBeaconUuidForTopic":true}
to
{"pubuuid4topic":true}

Note that OpenHAB discovery switch and auto-discovery switch will be replaced automatically with the new keys definition but the history between the keys will not be preserved.

Checklist:

• The pull request is done against the latest development branch
• Only one feature/fix was added per PR and the code change compiles without warnings
• I accept the DCO.