install: Enable bootprefix by default

This is the last bit necessary to enable installations to
systems without a separate `/boot` partition (as is true in
the default RHEL 9 AMIs).

I was too chicken to enable it by default in ostree long ago;
and now here we are.  Should definitely enable it in ostree,
but let's do it here now.

Signed-off-by: Colin Walters <walters@verbum.org>

lib/src/install.rs

@@ -466,6 +466,9 @@ async fn initialize_ostree_root_from_self(
     };
     for (k, v) in [
         ("sysroot.bootloader", bootloader),
+        // Always flip this one on because we need to support alongside installs
+        // to systems without a separate boot partition.
+        ("sysroot.bootprefix", "true"),
         ("sysroot.readonly", "true"),
     ] {
         Task::new("Configuring ostree repo", "ostree")