Permit download of the hashing schema from the server

[nbgl]

Currently, Anonlink requires a Clkhash schema for a project, even though it doesn’t use it. This is an opportunity to enforce consistent hashing schemas between parties.

I propose that we permit parties to download the schema from the Entity Service. This download can happen in the Clkhash CLI tools. Clkhash could then ensure that the hashing conforms to the schema, before uploading it to the server.

This proposal requires an API change in the Entity Service.

Related to data61/clkhash#151.

[wilko77]

endpoint /projects/{project_id}: get returns among other things also the schema.
However, there is currently an open issue (#197) around the access permission for this endpoint.

[nbgl]

Indeed it does! I missed that.

I’ll keep this issue open to complement #197: we need the permissions relaxed to make this work.