helpers: support rdm version detection from ref

[tmorrell]

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Description

This adds the ability for invenio-cli to look at the "ref" variable of the Pipfile, which is used when directly referencing repos on GitHub like

invenio-app-rdm = {git = "https://github.com/caltechlibrary/invenio-app-rdm.git", ref = "v13.0.0b1.dev17.caltech.v2", extras = ["opensearch2", "s3"]}

Checklist

Ticks in all boxes and 🟢 on all GitHub actions status checks are required to merge:

• I'm aware of the code of conduct.
• I've created logical separate commits and followed the commit message format.
• I've added relevant test cases.
• I've added relevant documentation.
• I've marked translation strings.
• I've identified the copyright holder(s) and updated copyright headers for touched files (>15 lines contributions).
• I've NOT included third-party code (copy/pasted source code or new dependencies).
  • If you have added third-party code (copy/pasted or new dependencies), please reach out to an architect.

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