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>

userdocs/contributing/debugging.rst

@@ -239,7 +239,7 @@ Example debugging session
    altvalue: []string len: 0, cap: 0, nil,
    from: "",
    def: []string len: 0, cap: 0, nil,},
-   ContainerName: github.com/warewulf/warewulf/internal/pkg/node.Entry {
+   ImageName: github.com/warewulf/warewulf/internal/pkg/node.Entry {
    value: []string len: 0, cap: 0, nil,
    altvalue: []string len: 0, cap: 0, nil,
    from: "",