Include Project-URLs in `pip show` output

[jwodder]

What's the problem this feature will solve?

A growing number of packages record URLs for things like their source repository and documentation using Project-URL metadata, yet pip show currently does not output these values, not even when --verbose is supplied. pip show does output the Home-page URL, but given that PEP 621 drops support for specifying this metadata field in favor of using Project-URLs instead, the number of packages that have Project-URLs but no Home-page is only going to grow.

Describe the solution you'd like

pip show packagename should include in its output each Project-URL from the given project's metadata in a form like:

Name: pip
Version: 21.3.1
Summary: The PyPA recommended tool for installing Python packages.
Home-page: https://pip.pypa.io/
Project-URL: Documentation, https://pip.pypa.io
Project-URL: Source, https://github.com/pypa/pip
Project-URL: Changelog, https://pip.pypa.io/en/stable/news/
Author: The pip developers
Author-email: distutils-sig@python.org
License: MIT
Location: /usr/local/lib/python3.9/site-packages
Requires: 
Required-by: pip-run, pipdeptree

If a project has no Project-URLs, no Project-URL fields will be emitted.

Alternative Solutions

• The --verbose option could be required in order to display Project-URLs
• Rather than outputting each Project-URL in a separate field, something similar to how pip show -v shows classifiers could be done:

Name: pip
Version: 21.3.1
Summary: The PyPA recommended tool for installing Python packages.
Home-page: https://pip.pypa.io/
Project-URLs:
  Documentation, https://pip.pypa.io
  Source, https://github.com/pypa/pip
  Changelog, https://pip.pypa.io/en/stable/news/
Author: The pip developers
Author-email: distutils-sig@python.org
License: MIT
Location: /usr/local/lib/python3.9/site-packages
Requires: 
Required-by: pip-run, pipdeptree

Additional context

N/A.

Code of Conduct

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