Add support for Pydantic 2 non-destructively

[frost-nzcr4]

I've found implementations here on PR, but they all contain disruptive changes that make Pydentic 2 mandatory or define new functions without tests. I propose to implement this support in a non-destructive and unobtrusive way, while maintaining as much backward compatibility as possible.

All you need is to set extras in fastapi-utils or pin the pydantic dependency in your project:

• for v1 use fastapi-utils = "^0.3", or pydantic = "^1.10", or both,
• for v2 use fastapi-utils = { version = "^0.3", extras = ["pydantic_settings"] }, or pydantic = "^2.0", or both.

Tested in my projects with Pydantic v1 on Python 3.10, and Pydantic v2 on Python 3.11 & 3.12.

Fix #276

[yuval9313]

I liked it very much, however in the new version (soon to be released 0.6.0) we will support pydantic 2.0, leave this around so I can test it to version 1.0