Add Synth Labs Solo

[hongaaronc]

Description

This PR adds VIA support for the Synth Labs Solo macropad. This is a 7-key macropad with remappable rotary encoder support. The macropad layout has a total of 14 hotswap sockets, to allow the layout to be reversible (7 sockets for each orientation).

In VIA, the remappable rotary encoder is represented as 3 keys (CW rotation key, CCW rotation key, press key). The reversible layout is able to be adjusted via a "Knob" dropdown in the "Layouts" tab with 2 options - "Left" or "Right".

More info on the macropad is available here:
https://geekhack.org/index.php?topic=115880.0

QMK Pull Request

qmk/qmk_firmware#16103

Checklist

• The VIA support for this keyboard is in QMK master already (MANDATORY)
• The VIA definition follows the guide here: https://caniusevia.com/docs/layouts
• I have tested this keyboard definition using VIA's "Design" tab.
• I have tested this keyboard definition with firmware on a device.
• I have assigned alpha keys and modifier keys with the correct colors.
• The Vendor ID is not 0xFEED

[yiancar]

Cheers thanks!