add support for volumes

Signed-off-by: Avi Deitcher <avi@deitcher.net>

examples/volumes.yml

@@ -0,0 +1,45 @@
+# example with volumes, both blank and populated
+kernel:
+  image: linuxkit/kernel:6.6.13
+  cmdline: "console=tty0 console=ttyS0 console=ttyAMA0"
+init:
+  - linuxkit/init:8a7b6cdb89197dc94eb6db69ef9dc90b750db598
+  - linuxkit/runc:6062483d748609d505f2bcde4e52ee64a3329f5f
+  - linuxkit/containerd:e7a92d9f3282039eac5fb1b07cac2b8664cbf0ad
+  - linuxkit/ca-certificates:5aaa343474e5ac3ac01f8b917e82efb1063d80ff
+onboot:
+  - name: sysctl
+    image: linuxkit/sysctl:5a374e4bf3e5a7deeacff6571d0f30f7ea8f56db
+  - name: dhcpcd
+    image: linuxkit/dhcpcd:e9e3580f2de00e73e7b316a007186d22fea056ee
+    command: ["/sbin/dhcpcd", "--nobackground", "-f", "/dhcpcd.conf", "-1"]
+onshutdown:
+  - name: shutdown
+    image: busybox:latest
+    command: ["/bin/echo", "so long and thanks for all the fish"]
+services:
+  - name: getty
+    image: linuxkit/getty:5d86a2ce2d890c14ab66b13638dcadf74f29218b
+    env:
+     - INSECURE=true
+  - name: rngd
+    image: linuxkit/rngd:cdb919e4aee49fed0bf6075f0a104037cba83c39
+  - name: nginx
+    image: nginx:1.19.5-alpine
+    capabilities:
+     - CAP_NET_BIND_SERVICE
+     - CAP_CHOWN
+     - CAP_SETUID
+     - CAP_SETGID
+     - CAP_DAC_OVERRIDE
+    binds:
+     - /etc/resolv.conf:/etc/resolv.conf
+     - blank:/blank
+     - alpine:/alpine
+volumes:
+- name: blank   # blank volume
+- name: alpine  # populated volume
+  image: alpine:3.19
+files:
+  - path: etc/linuxkit-config
+    metadata: yaml