Use more complex activation wrapper and add workaround for deploy-rs#185

[notgne2]

There has to be a better way, but this should work around https://github.com/serokell/deploy-rs/issues/185 for now, I've tested it on my own system and I am able to successfully boot with systemd-initrd for the first time. This could have been a smaller patch but I also wanted to change the way the activatable- wrapping works to be be a little more sneaky and hopefully trip things up a little less.

[notgne2]

To make it more discoverable, these both fix it upstream: https://github.com/NixOS/nixpkgs/pull/209829 https://github.com/NixOS/nixpkgs/pull/210505 - extra investigation into other bootloader builders might also be a good idea.

imo regardless of upstream fixes we should still do the more complex wrapper, but if all goes well upstream we can drop the workaround part of this patch.

[rvem]

@notgne2, may I ask you to squash and rebase your branch before merging?