Set Pydantic 2.* as possible dependency

[EugeneLagonski]

Description
Pydantic was updated to the 2nd version but the library pins it to the 1st version. I checked the latest pydantic version (2.8.2) and all tests passed. (also successfully tested the Pydantic 2.0.0)

It's needed to minimize version conflicts in environments.

Related issue: #3617

Steps to reproduce

$git clone https://github.com/aws/serverless-application-model.git
$ cd serverless-application-model
$ python3 -m venv _e
$ . _e/bin/activate
(_e) $ pip install "-e .[dev]"
(_e) $ pip install pydantic==2.8.2
(_e) $ make test

Observed result

(_e) $ pip install pydantic==2.8.2
(_e) $ make test
Required test coverage of 95% reached. Total coverage: 95.85%

================================================================= 3988 passed in 72.79s (0:01:12) =================================================================

Additional environment details
OS: MacOS Sonoma 14.6.1 aarch64
If using the SAM CLI, sam --version: N/A
AWS region: N/A

[github-actions]

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[EugeneLagonski]

Closing had an outdated version in the env where it was an issue