[Keyboard] Add TGR x SINGA Unikorn 60 (#6249)

* initial commit, copied from singa

* default 60_ansi LAYOUT implemented and tested workin

* add rgb underglow support bounded by ifdefs

* edit readme to provide information on reset procedure and on rgb underglow support

* improve the default keymap to have a second layer with function keys and even a RESET

* Add LAYOUT_all macro and discovered that split backspace uses an additional pin on the microcontroller

* fix up last line in readme

* Add QMK Configurator support