Automate/sync pyopds2 pydantic models (based on readium web manifest publication schema)

https://drafts.opds.io/opds-2.0.html#appendix-a-json-schema

pyopds2 should implement a pydantic model for each of the following:
https://github.com/opds-community/drafts/tree/main/schema
https://github.com/readium/webpub-manifest/tree/master/schema

@HadrienGardeur can you help us understand the difference between these two links?

As part of this issue, we can write a script that programatically runs code gen (https://docs.pydantic.dev/latest/integrations/datamodel_code_generator) versus the opds schema files.

Start by comparing the OPDS drafts schema and Readium web publication manifest schema linked in the issue, then review datamodel-code-generator's Pydantic integration. Define the model coverage and schema differences before implementing generation; done means each requested schema has a Pydantic model and a script can run the code generation process.

Written by the indexing model from the issue text.