feat: stamp the "tag" attribute for oci_push

[nguyening]

Motivation

I want to tag my OCI images in oci_push with some values from a stable status file. Currently we do contortions using a repo rule to accomplish this

load("@metadata//:metadata.bzl", "git_sha") # read the value of GIT_COMMIT_SHA

oci_push(
    tag = "v1000-{}".format(git_sha)
    # ...
)

which is not cache friendly. rules_docker supports this inside its pusher binary.

Changes

• OCIReferenceInfo can have an attr "tag_file" set to a file with expanded content of tag
• The contents of oci_push.tag can be expanded with status file kv's

Testing

[joneshf-dd]

This is great! Thanks for doing this!

[joneshf-dd]

💭 thought: Not really something to block on, but as a heads up: it looks like these code blocks don't get rendered properly in the Markdown. I don't think it's worth blocking on because Markdown inside of tables likely requires an update to our dependencies that includes this change: bazelbuild/stardoc#167.

[nguyening]

Nice! I can give upgrading a try in a separate PR if this is expected to work