Make MACROS___make_metadata_table to use schema

[yarikoptic]

ATM we duplicate values from schema into calls to MACROS___make_metadata_table, e.g. in

bids-specification/src/modality-agnostic-files.md

Line 21 in 5b4b0fd

Every dataset MUST include this file with the following fields:

<!-- This block generates a metadata table.
The definitions of these fields can be found in
  src/schema/objects/metadata.yaml
and a guide for using macros can be found at
 https://github.com/bids-standard/bids-specification/blob/master/macros_doc.md
-->
{{ MACROS___make_metadata_table(
   {
      "Name": "REQUIRED",
      "BIDSVersion": "REQUIRED",
      "HEDVersion": "RECOMMENDED",
      "DatasetLinks": "REQUIRED if [BIDS URIs][] are used",
      "DatasetType": "RECOMMENDED",
      "License": "RECOMMENDED",
      "Authors": "RECOMMENDED if CITATION.cff is not present",
      "Acknowledgements": "OPTIONAL",
      "HowToAcknowledge": "OPTIONAL",
      "Funding": "OPTIONAL",
      "EthicsApprovals": "OPTIONAL",
      "ReferencesAndLinks": "OPTIONAL",
      "DatasetDOI": "OPTIONAL",
      "GeneratedBy": "RECOMMENDED",
      "SourceDatasets": "RECOMMENDED",
   }
) }}

for dataset_description.json although that all is prescribed in https://github.com/bids-standard/bids-specification/blob/HEAD/src/schema/rules/dataset_metadata.yaml which also hints on that above is not entirely "complete" - some fields might be REQUIRED whenever above RECOMMENDED for some types of packages, and misses Genetics altogether.

As duplication is source of all kinds of bugs, I think we should strive to automate generation there, pretty my via smth like MACROS___make_metadata_table_for_path(path == "/dataset_description.json") . I am not yet sure yet how feasible to fully automate across all possible conditions etc, just stating that we should look into it ;-)