Adding OpenWrt Support for Netgear RAX120 (Nighthawk AX12)

Not yet.

I bought RAX120 (v1) a few months ago, but I haven't done much for it before the v1/v2 difference became known. (I have mainly waited that some ath11k support & possibly the Xiaomi ax3600 support would be merged.)

but I added the basic info into wiki:

(also the advice how to open the box to attach the serial cable for debugging. Opening is pretty tough...)