Support of multiple inverters

[KFU141]

It would be great to have an option that the publisher can handle multiple inverters at the same time.

[flohoff]

Topic is not the only issue here - One of the real problems is the fixed client id when connecting the MQTT broker which causes the first instance of hms-mqtt-published to be disconnected.

And just suffixing the client id is also a problem as some brokers limit for client id uniqueness is 23 byte - when simply appending the process.id it will be outside of the 23 bytes with the current scheme.