The OCI distribution spec only allows lower case letter in container repository (#2252)

name
(https://github.com/opencontainers/distribution-spec/blob/main/spec.md#pulling-manifests),
this doesn't bode well with Bazel package path using upper case.

To be clear: docker itself is ok with upper case:
https://ktomk.github.io/pipelines/doc/DOCKER-NAME-TAG.html.

Picking the common denominator here, and force lower case on pkg path.

Author: sfc-gh-bxin

container/image.bzl

@@ -237,12 +237,12 @@ def _repository_name(ctx):
     """Compute the repository name for the current rule."""
     if ctx.attr.legacy_repository_naming:
         # Legacy behavior, off by default.
-        return _join_path(ctx.attr.repository, ctx.label.package.replace("/", "_"))
+        return _join_path(ctx.attr.repository, ctx.label.package.lower().replace("/", "_"))
 
     # Newer Docker clients support multi-level names, which are a part of
     # the v2 registry specification.
 
-    return _join_path(ctx.attr.repository, ctx.label.package)
+    return _join_path(ctx.attr.repository, ctx.label.package.lower())
 
 def _assemble_image_digest(ctx, name, image, image_tarball, output_digest):
     img_args, inputs = _gen_img_args(ctx, image)