[ENG-1984] static schema

[aaxelb]

what

add a static definition of the SHAREv2 schema, so we can start trimming tangles around all the ShareObject models

• share/schema/schema-spec.yaml contains the barest info actually needed by other code (mostly share.util.graph and share.models.validators)
• share.schema.shapes defines how the schema info will be structured
• share.schema.loader loads that yaml file and puts it in those structured shapes
• share.schema.ShareV2Schema ties the above together -- this is what consumers will import and use

deliberate deviations

things that are meaningfully different from the model-based SHAREv2 schema

• remove ThroughContributors (and Contributor.contributed_through) -- there are exactly 0 of these on production
• all fields are defined on the concrete type
  • some fields in the model-based schema are only valid for specific subtypes -- this loosens that constraint
  • this simplifies things but could allow some slightly weird-looking data through
  • affected fields:
  • on AbstractAgent:
    • Person.given_name
    • Person.family_name
    • Person.additional_name
    • Person.suffix
  • on AbstractCreativeWork:
    • Registration.registration_type
    • Registration.withdrawn
    • Registration.justification
  • on AbstractAgentWorkRelation:
    • Creator.order_cited
    • Funder.awards

TODO

• [x] basic tests (¿is the schema "correct"?)
  • [x] creative works
  • [x] agents
  • [x] tags/subjects
  • [x] relations
• [x] SchemaLoader unit tests

jira: ENG-1984