PE-7481: add /boot as default bind mount for uki (#454)

Author: nianyush

Earthfile

@@ -666,7 +666,6 @@ base-image:
 
     IF [ "$IS_UKI" = "true" ]
         # create empty boot directory to support services like longhorn which require /boot
-        RUN mkdir -p /boot
         COPY cloudconfigs/80_stylus_uki.yaml /system/oem/80_stylus_uki.yaml
     END
 

cloudconfigs/80_stylus_uki.yaml

@@ -1,5 +1,10 @@
 #cloud-config
 stages:
+  rootfs:
+    - name: "custom mounts"
+      environment_file: /run/cos/cos-layout.env
+      environment:
+        CUSTOM_BIND_MOUNTS: "/boot"
   initramfs:
     - if: '[ -e "/run/cos/uki_boot_mode" ] && [ ! -f "/run/cos/live_mode" ]'
       name: link agent provider stylus