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/pkg/node/fields_test.go

@@ -114,7 +114,7 @@ func Test_listFields(t *testing.T) {
 				"Profiles",
 				"Comment",
 				"ClusterName",
-				"ContainerName",
+				"ImageName",
 				"Ipxe",
 				"RuntimeOverlay",
 				"SystemOverlay",
@@ -168,7 +168,7 @@ func Test_listFields(t *testing.T) {
 				"Profiles",
 				"Comment",
 				"ClusterName",
-				"ContainerName",
+				"ImageName",
 				"Ipxe",
 				"RuntimeOverlay",
 				"SystemOverlay",