[Keyboard] Add YDKB Mountain

[Wraul]

This keyboard comes with a YDKB firmware that can be configured using the tool at https://ydkb.io/ But I want to use QMK with all my keyboards, so here we are.

Description

Mapping the PCB matrix was a bit of a pain as it uses multiple 74HC595 shift registers, which I never worked with before. But after some reverse enginering and looking at the YDKB firmware I have something that works. Please let me know if there is something that could be done better.

I used the same USB PID and VID as the YDKB firmware. This might be a good thing or maybe I shouldn't do that?

Types of Changes

• [ ] Core
• [ ] Bugfix
• [ ] New feature
• [ ] Enhancement/optimization
• [x] Keyboard (addition or update)
• [ ] Keymap/layout/userspace (addition or update)
• [ ] Documentation

Checklist

• [x] My code follows the code style of this project: C, Python
• [x] I have read the PR Checklist document and have made the appropriate changes.
• [ ] My change requires a change to the documentation.
• [ ] I have updated the documentation accordingly.
• [x] I have read the CONTRIBUTING document.
• [ ] I have added tests to cover my changes.
• [ ] I have tested the changes and verified that they work and don't break anything (as well as I can manage).