make it easier to interpolate artifact names

[cburroughs]

Is your feature request related to a problem? Please describe.

Right now it is easy to tell pants to "package all the things" with pants package ::. This fills up dist with all of the goodies. However, instead of having foo.tar.gz I'd like to have foo-VERSION.tar.gz so that everything is ready for uploading publishing. (Where version is maybe a constant like v.1.2.3 or just the git sha.)

output_path can almost do that, but then I have to re-implement the / --> . logic.

output_path
    type: str | None
    default: None

    Where the built asset should be located.
    
    If undefined, this will use the path to the BUILD file, followed by the target name. For example, `src/python/project:app`
    would be `src.python.project/app.ext`.
    
    When running `pants package`, this path will be prefixed by `--distdir` (e.g. `dist/`).
    
    Warning: setting this value risks naming collisions with other package targets you may have.

Describe the solution you'd like
Give all "just a file" artifacts an output_name to go along with output_path, the "path to output" logic then looks something like:

• default: build_file_dir.replace('/', '.') + name
• if output_name is set: build_file_dir.replace('/', '.') + output_name
• if output_path is set: `output_Path

Describe alternatives you've considered

• set the target name to something dynamic like "foo + git_sha". Quick and dirty but then the name changes on every commit.
• Write a versioned_tarball macro.

Additional context
Doing it with a macro isn't that bad. But I feel like there is some fundamental inconsistency where some "packages" like docker or python_distributions have a separate "version", but others do not.

spinoff from: https://pantsbuild.slack.com/archives/C0D7TNJHL/p1680240146011409

[tdyas]

The challenging part of this request is probably the migration path for users who are setting the path and filename using output_path. If the semantics for output_path change to only be the path, then the output filename for existing users will change if they do not also update output_name.

Alternative solution: Keep only the output_path field, but define string replacements for the normalized directory ("spec path" in Pants parlance) and normalized target name. The default then becomes something like "{normalized_spec_path}/{normalized_target_name}" but with some provision made for the file suffix (e.g., .pex).

[tdyas]

@cburroughs: #21175 is a draft solution. Let me know if the shape of it works for you.

[cburroughs]

The template approach looks reasonable to me, and I like having fewer fields. Thank you.

[tdyas]

Implemented by #21175.