add optional keyring dependency target in pyproject.toml

[deronnax]

Hello.
Thank you very much for PDM, incredible work, much appreciated here.

We are considering recommending PDM for the whole company, but we would very much need our contributors being able to install PDM "the right way" (meaning: with keyring included from the start) in one go, simply (and not having to run pip install keyring or pipx inject pdm keyring afterward), because we really value the password being stored in a safe way. And what comes with the all optional dependencies really looks irrelevant and cumbersome for our use case.
We think keyring is a very, very import dependency. For comparison, Poetry made it mandatory.

If you think it's worth an entry in the NEWS file, I will fill one.

Thank you very much.

[frostming]

Appreciated if you can do more changes:

• Make truststore in its own group
• Make copier and cookiecutter in their own groups, separately, and template group to contain both: pdm[copier,cookiecutter]
• Change all to include all optional groups, by referencing the names.

[deronnax]

done. Tell me if it suits you.