Establish a standard way for *clients* to provide additional metadata to the crate

[elichad]

A client could host a metadata file at a defined location which contains an RO-Crate "fragment" - i.e. a set of JSON-LD entities which should be added to the generated crate to represent the client.

e.g. host organisation, location, TRE details, responsible people (from the Fed-A-Crate use case)