overlay: add support for locale directory

inconveniently locales are in /usr/lib/locale rather than var.
selectively overlay it with a subvolume

mkosi.extra/usr/bin/_calamares@subvol

@@ -28,6 +28,7 @@ cd "$tmpdir"
 rm -rfv ./*
 btrfs send "/system/@kdeos_$IMAGE_VERSION" | btrfs receive .
 btrfs subvolume create @home
+btrfs subvolume create @locale
 btrfs subvolume create @snap
 btrfs subvolume create @var-overlay
 btrfs subvolume create @etc-overlay

mkosi.extra/usr/bin/_kdeos-overlay

@@ -27,6 +27,9 @@ mount -v \
 mount -v \
     -o rw,subvol=@home \
     "$rootdisk" "${sysroot}/home"
+mount -v \
+    -o rw,subvol=@locale \
+    "$rootdisk" "${sysroot}/usr/lib/locale"
 mount -v \
     -o rw,subvol=@snap \
     "$rootdisk" "${sysroot}/snap"

mkosi.repart/50-root.conf

@@ -13,6 +13,9 @@ SplitName=root
 Subvolumes=/@home
 MakeDirectories=/@home
 
+Subvolumes=/@locale
+MakeDirectories=/@locale
+
 Subvolumes=/@snap
 MakeDirectories=/@snap