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>

internal/app/wwctl/overlay/build/main_test.go

@@ -17,7 +17,7 @@ func Benchmark_Overlay_Build(b *testing.B) {
 		`nodeprofiles:
   default:
     comment: This profile is automatically included for each node
-    container name: rockylinux-9
+    image name: rockylinux-9
     ipxe template: default
     runtime overlay:
       - hosts