* [FIRSTBOOT] refactor code:
-auto-detect all possible variants in firstboot
- DRY script code
- add $RESIZE_COMMENCED , $BITTBOY_CONFIG , $MIYOO_CONFIGvariable
- add debug log before any shutdown
- don't `export` env var if not needed
- move and use $DETECTED auto_ID variants on II Test_Block
- cleanup + add more descriptions
- add Test_Flip prompt for double check on Test Video (only if enduser selected "Flipped!" at first test)
- remove useless SWAP & MAIN part. mount
- add safety read-only for /boot before shutdown
* [BOARD] add gmenu2x inputs inputs with `manifest`
- update genimage config with `input_bittboy.conf` and `input_miyoo.conf`
* [README] Add flashing procedure schematic (made in draw.io)
