Allow volatile and stable status info in `maven_coordinates`

[AustinSchuh]

I'd like to be able to do something equivalent to:

maven_export(
    name = "wpiutil-java_publish",
    lib_name = "wpiutil-java",
    maven_coordinates = "edu.wpi.first.wpiutil:wpiutil-java:2025.424242.3.1-$(BUILD_TIMESTAMP)-$(BUILD_EMBED_LABEL)",
)

[AustinSchuh]

Digging in to how other rule sets do this, rules_oci does this by using https://github.com/bazel-contrib/bazel-lib/blob/main/docs/expand_template.md to provide a file with the tags.

[shs96c]

Typically I've done this with a repo rule which stores this information is a constant, which can then be accessed from anywhere.

[AustinSchuh]

That would work too. Do you have an example or a link to what starlark calls to use to do that? I tried to get access to those two files from starlark in a repo rule and failed. I kept learning that they are only available in actual rules, and even there, only as files.

[shs96c]

You may need to something funky like execute the workspace status script from the repo rule, capture the output, and do some processing of that.