Add Keychron C1 RGB support.

[NetUserGet]

Update Keychron C1 RGB support from sn32_master.

Description

Full support for RGB, status indicators, and dip switch.

Types of Changes

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

Issues Fixed or Closed by This PR

Checklist

• My code follows the code style of this project: C, Python
• 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.
• 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).

[dexter93]

nice work!

Following the keychron structure, this should change to c1/rgb/ ( there are other variants with a different chip). Please see other merged K* keyboards.

Also a bonus, it's a good idea to fix the LED flags - https://github.com/SonixQMK/qmk_firmware/blob/sn32_develop/docs/features/rgb_matrix.md#flags-flags 4 is only on alphas, mods need a different flag