[airbyte-protocol]: Add support for Pydantic v2, with backward-compatible test for Pydantic v1

[aaronsteers]

This library (airbyte-protocol-models) is depended upon by the Python CDK, which is depended upon by PyAirbyte, which is depended upon by user environments with a variety of other installed libraries.

Users have asked to relax the Pydantic requirement so we can allow PyAirbyte in environments that also need Pydantic 2.0 (directly or by transitive dependencies).

Proposed actions:

1. Relax the Pydantic version constraints to allow Pydantic 2.0.
2. Add a CI test matrix to ensure we're validating successful execution in 1.x as well as 2.x.
3. Repeat this process on the CDK, and then also in PyAirbyte:
   1. [cdk] Upgrade Airbyte and its dependencies to Pydantic V2 airbyte#36475
   2. Support of Pydantic v2  PyAirbyte#216

Migration guide is here: https://docs.pydantic.dev/latest/migration/

[aaronsteers]

Resolved by:

• feat: publish new pydantic v2 version of python protocol, temporarily alongside pydantic v1 version #81

cc @erohmensing