Modify gatewayRF auto discoverability

[JamiePhonic]

Description:

Pass switchRF[0] as the subtype argument to announceDeviceTrigger() which will cause recieved codes to be picked up by home assistant as triggers, i.e. When setting up automations in Home Assistant, selecting a device trigger and an OMG device will allow the user to select a code picked up during the autoDiscover window as the trigger for the automation, for example "1394004" pressed

Also change getUniqueId() call to remove leading '-' which will prevent MQTT topics having '--' in them

Checklist:

• [x] The pull request is done against the latest development branch
• [x] Only one feature/fix was added per PR and the code change compiles without warnings
• [x] I accept the DCO.

[JamiePhonic]

Closing becasue this needs some more work. Triggers seem to be inconsistent.