DDF improvement for button chords on Illumra Dual Rocker Switch (PTM215ZE Friends of Hue)

[lowellstewart]

First of all, huge thanks to everyone (especially @mdolnik) involved in adding the initial support for this switch back in 2020. I've had one sitting in a bin and I finally got it working today thanks to PR #3285 !

I knew from previous experiments with this switch, that in addition to the 4 buttons already implemented, the switch also supports undocumented button "chords", through which additional automations can be assigned. See the stellar research user rkjnsn did here: https://www.reddit.com/r/Hue/comments/8s85g7/experience_with_illumra_rocker_switch_and_hue/

Using the additional codes listed there, I added support for 4 additional "virtual" buttons on the Illumra Dual Rocker switch, which are accessed by pushing two of the other buttons simultaneously:

• Button 5 == Button 1 (left top) + Button 3 (right top)
• Button 6 == Button 2 (left bottom) + Button 3 (right top)
• Button 7 == Button 1 (left top) + Button 4 (right bottom)
• Button 8 == Button 2 (left bottom) + Button 4 (right bottom)

It may be kind of arcane, but it could be a cool easter egg. ;-) It's a very limited change thankfully.