Set device_class to duration in HA sensor definitions

[heennkkee]

Is your feature request related to a problem? Please describe.
When automatically detecting devices through MQTT in Home Assistant the uptime counters could have their device_class set to duration. I believe that the unit_of_measurement would also need to be changed from minutes to min.
This effects how the values are rendered by default in HA, and although I honestly prefer the way the default rendering for the values are "as is", flagging the values with the correct attributes are more correct and "future proofer".

With device_class set:

Existing settings:

Describe the solution you'd like
The above one

Describe alternatives you've considered
To ignore this and keep going as is works just fine, but thought this was an improvement.

Additional context
None

[proddy]

I'll test it out, thanks for submitting.

[proddy]

looks like HA does use "min" https://github.com/home-assistant/core/blob/e2e272aeb6b957cc34ca4d58b9e9c69b002a12f4/homeassistant/const.py#L592