[ENH] Implement pipeline create subcommand

[mathdugre]

• Closes [ENH] Add nipoppy pipeline subcommands #554
• Closes [ENH] Implement nipoppy pipeline create #569

Changes proposed in this pull request:

• Create a template pipeline bundle to facilitate pipeline development.
• Allow bundle to be create from an existing boutiques descriptor.

Checklist (for reviewers)

This section is for the PR reviewer

• PR has an interpretable title with a prefix (e.g. [BUG], [DOC], [ENH], [MAINT])
  Refer to NumPy Development Guide for a full list
• PR links to GitHub issue with mention Closes #XXXX
• Tests pass
• Checks pass

For new features:

• Tests have been added

For bug fixes:

• There is at least one test that would fail under the original bug conditions

---

📚 Documentation preview 📚: https://nipoppy--636.org.readthedocs.build/en/636/

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

Files with missing lines	Coverage Δ
nipoppy/cli.py	100.00% <100.00%> (ø)
nipoppy/utils.py	98.76% <100.00%> (+<0.01%)	⬆️
nipoppy/workflows/pipeline_store/create.py	100.00% <100.00%> (ø)

... and 6 files with indirect coverage changes

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[michellewang]

🧑‍🍳