Package make-initrd-propagator: Information

- time limit for rw slice mkfs extended to 3s

- improve RW slice operation (closes: #32476, #32562):
  only create/use it when there's enough space (1Gb or more), and
  it's been either
  + explicitly asked for (BIOS mode), or
  + fast enough (UEFI mode; otherwise the filesystem
    will be marked "alt-slow-storage")
- add mkfs/mount options for faster operation
- extend debug support

- only mount rw slice when live_rw is specified explicitly
  due to severe I/O penalty coming with it (closes: #32476)
- slightly better package description