New module: accessions.json

[ESapenaVentura]

What is the proposed name of the new schema?
accessions.json

What field(s) should the new schema contain?

The fields would be the same as the ones stated in this file from a closed PR https://github.com/HumanCellAtlas/metadata-schema/blob/fa62af61db37e6d646387f7b8b7465082b9cbfb4/json_schema/module/external_identifier.json

Why is the new schema needed?

In order to easily prepare for new types accessions and simplify the schema, we need a generic way of indicating accessions. Hopefully, this new schema will allow for the use of identifiers.org to easily create links to the new accessions without having to hardcode URLs