Scarlet Bandana Layout Additions (qmk#20882)

* add matrix_diagram.md

* info.json: apply friendly formatting

* info.json: correct layout data

* rename LAYOUT_all to LAYOUT_65_xt_ansi_split_space_split_bs

* add LAYOUT_65_xt_ansi_split_space

* add LAYOUT_65_xt_ansi_split_bs

* add LAYOUT_65_xt_ansi

* update readme.md

- convert metadata section to list
- update Availability link (mark as "no longer available" as the vendor no longer ships)
- add Flashing and Bootloader instructions