bootctl: discover and pring global 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.

Support for /boot/efi/EFI/Linux/<UKI_NAME>.efi.extra.d is already present,
so now cover addons present in /boot/efi/loader/addons (global addons).

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

src/shared/bootspec.h

@@ -79,6 +79,8 @@ typedef struct BootConfig {
         BootEntry *entries;
         size_t n_entries;
 
+        BootEntryAddons global_addons;
+
         ssize_t default_entry;
         ssize_t selected_entry;
 
@@ -132,6 +134,7 @@ static inline const char* boot_entry_title(const BootEntry *entry) {
 
 int show_boot_entry(
                 const BootEntry *e,
+                const BootEntryAddons *global_addons,
                 bool show_as_default,
                 bool show_as_selected,
                 bool show_reported);