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>

etc/grub/chainload.ww

@@ -12,7 +12,7 @@ menuentry "Load specific configfile" {
     conf="(http,{{.Ipaddr}}:{{.Warewulf.Port}})/efiboot/grub.cfg?assetkey=${assetkey}"
     configfile $conf
 }
-menuentry "Chainload shim of container" {
+menuentry "Chainload shim from image" {
     shim="(http,{{.Ipaddr}}:{{.Warewulf.Port}})/efiboot/shim.efi?assetkey=${assetkey}"
     chainloader ${shim}
 }