bootctl: discover local UKI PE addons

bootctl: discover local UKI PE addons

An UKI final command line is not just made of the content of .cmdline,
but also from the addons that are inserted in
/boot/efi/EFI/Linux/<UKI_NAME>.efi.extra.d (local addons) and
/boot/efi/loader/addons (global addons).

Therefore bootclt "status" and "list" should also include these addons
when printing the UKI command line.

Right now, discover addons present in
/boot/efi/EFI/Linux/<UKI_NAME>.efi.extra.d.

Example output (assume UKI_NAME=devel):
$ bootctl
ukiCmdline: console=tty0 console=ttyS0
   localAddon: devel.efi.extra.d/rpm_addon.addon.efi
      cmdline: └─this is a normal addon
 finalCmdline: console=tty0 console=ttyS0 this is a normal addon