Add inverted config for digital outputs

[flyte]

In order to add topic suffixes such as /set_on_ms and /set_off_ms we need to make sure that 'on' does indeed turn on the device. /set has been able to handle this in the past using on_payload and off_payload but it doesn't cut the mustard for explicit on/off topics.

It makes more sense to just add an inverted config value for each digital output so that it can be handled once and for all while setting up the output configuration.