Add support for volumes-from, image volumes, init

This should complete Podmanv2's support for volume-related flags.
Most code was sourced from the old pkg/spec implementation with
modifications to account for the split between frontend flags
(volume, mount, tmpfs) and the backend flags implemented here.

Also enables tests for podman run with volumes

Signed-off-by: Matthew Heon <matthew.heon@pm.me>

pkg/specgen/container_validate.go

@@ -14,7 +14,7 @@ var (
 	// SystemDValues describes the only values that SystemD can be
 	SystemDValues = []string{"true", "false", "always"}
 	// ImageVolumeModeValues describes the only values that ImageVolumeMode can be
-	ImageVolumeModeValues = []string{"ignore", "tmpfs", "bind"}
+	ImageVolumeModeValues = []string{"ignore", "tmpfs", "anonymous"}
 )
 
 func exclusiveOptions(opt1, opt2 string) error {