Add support for long-term statistics sensors

[sefininio]

The entity node allows for creating binary_sensor, sensor and switch entities on the HomeAssistant instance via the Node-RED Companion.

HomeAssistant recently introduced Long-Term statistics sensors - those are needed, for example, to create sensors compatible with the new energy dashboard.

[sefininio]

I think it basically means adding the state_class prop to the home assistant config section of the node.

[zachowj]

#459 (comment)

[sefininio]

Oh sorry, I missed it's a dup.
Well, I tried adding the attribute and that works! Thanks!

[zachowj]

Added in v0.40.0