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/warewulfd/parser.go

@@ -63,8 +63,8 @@ func parseReq(req *http.Request) (parserInfo, error) {
 			ret.stage = "ipxe"
 		} else if stage == "kernel" {
 			ret.stage = "kernel"
-		} else if stage == "container" {
-			ret.stage = "container"
+		} else if stage == "image" {
+			ret.stage = "image"
 		} else if stage == "overlay-system" {
 			ret.stage = "system"
 		} else if stage == "overlay-runtime" {