Add multi-group linking support

[TD22057]

Currently the db-add command can only link matching groups on the controller and responder. Update it to pass a group for each. That way button 4 of a remote can be linked to button 2 of a keypad for example.

[TD22057]

NOTE: as part of this - be sure to review #7 which has all the info I've been able to find on how to set the link db data fields which are crucial to this. Summary:

Responder Records
Data 1 Link-specific data (e.g. On-Level)
Data 2 Link-specific data (e.g. Ramp Rates, Setpoints, etc.)
Data 3 responder group number being linked to (i.e. what group responds)

Controller Records
Data 1 Number of retries (Normally set to 03, FF = no retries, 00 = Broadcast for cleanup)
Data 2 0x00
Data 3 Set to the controller group number (not normally needed but some devices use this)

[TD22057]

Fixed. db-add command line arg (and corresponding MQTT commands) can now add multi-group links. So you can link button 4 on one keypad to button 3 on a different keypad. Command line tool also has nice inputs for on level and ramp rate which can be used.