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/flags/flags.go

@@ -0,0 +1,10 @@
+package flags
+
+import (
+	"github.com/spf13/cobra"
+)
+
+func AddContainer(cmd *cobra.Command, dest *string) {
+	cmd.Flags().StringVarP(dest, "container", "C", "", "Set image name (backwards-compatibility)")
+	cmd.Flags().Lookup("container").Hidden = true
+}