Increase openapi generator and requirement to pydantic v2
We are already using pydantic v2 in idhub. v1 is getting old, hence the generator now produces v2 code.
The get_module_structure of the new version is identical to the previous so actual changes should be limited to inside the client implementation and not need identitylib users to change.
To resolve dependency requirements for https://gitlab.developers.cam.ac.uk/uis/devops/iam/idhub/api/-/issues/90