Rename "container" to "image"

- Updated `wwctl upgrade` to handle updates
- Maintained `.Container` and `.ContainerName` in tstruct
- Added `ContainerName()` methods to node and profile objects
- Added `--container`, `-C` aliases to wwctl commands (`<node|profile> <add|set>`)
- Added `wwctl container` alias
- Added support for `container_exit.sh` if `image_exit.sh` is not found

Signed-off-by: Jonathon Anderson <janderson@ciq.com>

dracut/modules.d/90wwinit/load-wwinit.sh

@@ -3,7 +3,7 @@
 info "Mounting tmpfs at $NEWROOT"
 mount -t tmpfs -o mpol=interleave ${wwinit_tmpfs_size_option} tmpfs "$NEWROOT"
 
-for archive in "${wwinit_container}" "${wwinit_system}" "${wwinit_runtime}"
+for archive in "${wwinit_image}" "${wwinit_system}" "${wwinit_runtime}"
 do
     if [ -n "${archive}" ]
     then