sysupdate: Add partial/pending flags to UpdateSet

This commit adds the flags and some basic formatting/printing of them.
Following commits will integrate them into the update/acquire/install
logic.

`UPDATE_PARTIAL` is set if any of the instances in the `UpdateSet` are
partial, i.e. have been partially downloaded.

`UPDATE_PENDING` is set if any of the instances in the `UpdateSet` are
pending, i.e. have been acquired (downloaded) but not yet installed.

Signed-off-by: Philip Withnall <pwithnall@gnome.org>
Helps: https://github.com/systemd/systemd/issues/34814

src/sysupdate/sysupdate-update-set-flags.h

@@ -10,6 +10,8 @@ typedef enum UpdateSetFlags {
         UPDATE_OBSOLETE   = 1 << 3,
         UPDATE_PROTECTED  = 1 << 4,
         UPDATE_INCOMPLETE = 1 << 5,
+        UPDATE_PARTIAL    = 1 << 6,
+        UPDATE_PENDING    = 1 << 7,
 } UpdateSetFlags;
 
 const char* update_set_flags_to_color(UpdateSetFlags flags);