Add examples with DatasetType = "project"

[yarikoptic]

Added to complement

• Add DatasetType="project" and rework existing "layout" example into a proper BIDS dataset bids-specification#1861

TODOs

• Examples
  • nipoppy inspired -- 1 is enough
    • finish tune up to correspond to [WIP] [ENH]: Add BIDS study layout nipoppy/nipoppy#687 . May be add scratch/ with it in .bidsignore ?
  • princeton inspired
  • YODA inspired
• Make it possible to skip validation using original validator (or even ensure that it must fail due to unknown value of DatasetType)
• Make sure deno validator is happy. Some related issues detected/filed
  • https://github.com/bids-standard/bids-validator/issues/2007
  • https://github.com/bids-standard/bids-validator/issues/2008
  • discuss ad-hoc error "There are no subject directories (labeled "sub-*") in the root of this dataset." Downgrade absence of sub- folders to warning bids-specification#1928 (not strictly necessary for this functionality since adding project limits validation to 'raw')
• Blocked by having Add DatasetType="project" and rework existing "layout" example into a proper BIDS dataset bids-specification#1861 merged first so validator could pick up that version

current bids-validator output with current version of the enh-project-datasettype at v1.10.0-35-g5f7004819

❯ deno run --allow-read --allow-env --reload -A https://github.com/bids-standard/bids-validator/raw/deno-build/bids-validator.js --schema file://$PWD/../bids-specification/schema-project.json proj-nipoppy
	[WARNING] UNKNOWN_BIDS_VERSION The BIDSVersion field of 'dataset_description.json' does not match a known release.
The BIDS Schema used for validation may be out of date.

		/dataset_description.json

	Please visit https://neurostars.org/search?q=UNKNOWN_BIDS_VERSION for existing conversations about this issue.

	[WARNING] JSON_KEY_RECOMMENDED A JSON file is missing a key listed as recommended.
		License
		/dataset_description.json

		GeneratedBy
		/dataset_description.json

		SourceDatasets
		/dataset_description.json

	Please visit https://neurostars.org/search?q=JSON_KEY_RECOMMENDED for existing conversations about this issue.


          Summary:                         Available Tasks:        Available Modalities:
          3 Files, 1.15 kB                                                              
          0 - Subjects 1 - Sessions                                                     

	If you have any questions, please post on https://neurostars.org/tags/bids.

[effigies]

Converting to draft since this is way behind the current spec.

[yarikoptic]

@asmacdo could you please tune it up to correspond to

• [WIP] [ENH]: Add BIDS study layout nipoppy/nipoppy#687 ?