main/postmarketos-mkinitfs: upgrade to 1.5

There was a fair bit of refactoring in this release to add support for ordering items in the initramfs archive, so some more independent testing of this before merging would be appreciated. I tested this version on the SHIFT 6mq and it was fine.

Also feedback from those working on #1618 (closed) would be helpful too 😄

Full changelog: https://gitlab.com/postmarketOS/postmarketos-mkinitfs/-/tags/1.5