Investigate json-schema and JSON-LD for specifying the metadata schema

Instead of implementing our own mechanism for specifying a JSON schema, should we just use https://json-schema.org/ ?

- Suresh: Some examples of JSON schema in scientific context - https://github.com/materials-data-facility/data-schemas/tree/master/schemas
- Suresh: Another option is to consider [JSON-LD](https://json-ld.org/). Particularly it will go well with [schema.org](https://schema.org/) vocabulary.
- Geoscience examples - https://github.com/ESIPFed/science-on-schema.org and https://geocodes.earthcube.org/#/landing
- https://github.com/psychoinformatics-de/datalad-hirni/pull/102

The investigation should evaluate what are the advantages to adopting either json-schema or JSON-LD. What do we get by adopting them over our own API approach? Also, where are they deficient? I imagine we'll still need some metadata schema definition API to specify things like the type of index to create, etc.

Start by comparing JSON Schema and JSON-LD using the examples and references linked in the issue, including schema.org and the scientific metadata projects. Document the advantages and deficiencies of each approach versus a custom API, including how index types would be specified. Done means the investigation records a recommendation and the remaining API requirements.

Written by the indexing model from the issue text.