[Feature Request] Support the customKeycodes property for user-defined keycodes

[mrnoisytiger]

Allow support for the customKeycodes property definable in the VIA JSON. See the following example for the JSON data structure:

"customKeycodes": [
    { "name": "A_CW", "title": "A_CW", "shortName": "A_CW" },
    { "name": "A_CCW", "title": "A_CCW", "shortName": "A_CC" },
    { "name": "B_CW", "title": "B_CW", "shortName": "B_CW" },
    { "name": "B_CCW", "title": "B_CCW", "shortName": "B_CC" },
    { "name": "C_CW", "title": "C_CW", "shortName": "C_CW" },
    { "name": "C_CCW", "title": "C_CCW", "shortName": "C_CC" },
...
  ],

Depends on #707.

See the following Discord conversation: https://discord.com/channels/802306358938435605/816488260250370080/1013662167859462204