Add support for attributes

[Pluimvee]

As not all telemetry deserves its own dedicated sensor, some detailed telemetry data would be stored in attributes. Most common use case is to add debug info, or aother less important sensor data as json object to one of the sensors

The code is minimized to publishing a string, which in fact for proper HA support should be a json object. However I think creating the json object should not be part of this library

[erkr]

Please accept the commits above. I like to have them as well

[dawidchyrzynski]

Hi @Pluimvee, thank you for your contribution. Could you please address the conflicts so that I can proceed with the merge?

[dawidchyrzynski]

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