Add JSON key for color temperature in Kelvin unit

[renne]

Is your feature request related to a problem? Please describe

The color temperature has to be entered in 'Mirek' unit. Average Joes see 'Kelvin' unit on the bulb package an have no idea what 'Mirek' unit is.

Describe the solution you'd like

I suggest a JSON key { "color": { "kelvin": <value> } } to set the color temperature in Kelvin unit.

Describe alternatives you've considered

Pointing average joes to the Zigbee2MQTT documentation and let them convert Mirek to Kelvin just causes confusion.

[github-actions]

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[Aragur]

Is it possible to reopen this issue?
I'm using NodeRED with the Google Assistant, the color temperature is only returned in Kelvin.
Or is there a formula I can use, to calculate Mirek to Kelvin?