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/profile/list/main_test.go

@@ -157,7 +157,7 @@ nodes:
     "Profiles": null,
     "Comment": "",
     "ClusterName": "",
-    "ContainerName": "",
+    "ImageName": "",
     "Ipxe": "",
     "RuntimeOverlay": null,
     "SystemOverlay": null,
@@ -209,7 +209,7 @@ nodes:
     "Profiles": null,
     "Comment": "",
     "ClusterName": "",
-    "ContainerName": "",
+    "ImageName": "",
     "Ipxe": "",
     "RuntimeOverlay": null,
     "SystemOverlay": null,
@@ -228,7 +228,7 @@ nodes:
     "Profiles": null,
     "Comment": "",
     "ClusterName": "",
-    "ContainerName": "",
+    "ImageName": "",
     "Ipxe": "",
     "RuntimeOverlay": null,
     "SystemOverlay": null,