Force label resolution of the distroless container image

By adding the call to Label(), we ensure that the label is resolved from
within the context of the bb-storage repository. This ensures that any
repositories depending on bb-storage will automatically pick it up.

tools/container.bzl

@@ -22,7 +22,7 @@ def multiarch_go_image(name, binary):
 
     oci_image(
         name = image_target,
-        base = "@distroless_static",
+        base = Label("@distroless_static"),
         entrypoint = ["/app/{}".format(native.package_relative_label(binary).name)],
         tars = [tar_target],
         # Don't build un-transitioned images, as the default target architecture might be unsupported