Add a kb2040 version of the onkey keyboard that works with the oled keymap

[jepler]

Description

The firmware built with qmk compile --keyboard handwired/onekey/kb2040 --keymap oled works with the Adafruit KB2040 "Kee Boar" & Stemma QT 128x32 OLED display.

To increase the number of I/O pins available in the Pro Micro form factor, Adafruit added a Stemma QT connector (compatible with SparkFun's Quiic connector, physically identical). The Adafruit part uses GP12/13 which corresponds to I2C peripheral 0 in the pico sdk numbering.

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.
• [x]I have tested the changes and verified that they work and don't break anything (as well as I can manage).