pydantic compatibility warning

[pjbull]

Actual migration to support 2.0.0 is going to be a bunch more work, so adding just the warning for the time being.

❯ pip list | grep pydantic
pydantic                   1.10.11

❯python
Python 3.11.4 (main, Jul  5 2023, 08:41:25) [Clang 14.0.6 ] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import cloudpathlib
>>> quit()

❯ pip install -U pydantic
...
Successfully installed pydantic-2.0.2

❯ python
Python 3.11.4 (main, Jul  5 2023, 08:41:25) [Clang 14.0.6 ] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import cloudpathlib
/Users/bull/code/cloudpathlib/cloudpathlib/__init__.py:49: PydanticVersionWarning: This version of cloudpathlib is only compatible with pydantic<2.0.0. You can ignore this warning if none of your pydantic models are annotated with cloudpathlib types.
  warn(PydanticVersionWarning(PydanticVersionWarning.message))

Docs preview:
https://deploy-preview-348--gallant-agnesi-5f7bb3.netlify.app/integrations/

[github-actions]

🚀 Deployed on https://deploy-preview-348--gallant-agnesi-5f7bb3.netlify.app

[codecov]

Codecov Report

Merging #348 (1bfb82c) into master (2a3d712) will decrease coverage by 0.3%.
The diff coverage is 70.0%.

Additional details and impacted files

@@           Coverage Diff            @@
##           master    #348     +/-   ##
========================================
- Coverage    94.2%   93.9%   -0.3%     
========================================
  Files          22      22             
  Lines        1484    1494     +10     
========================================
+ Hits         1399    1404      +5     
- Misses         85      90      +5     

Impacted Files	Coverage Δ
cloudpathlib/__init__.py	87.5% <70.0%> (-12.5%)	⬇️

... and 1 file with indirect coverage changes

[pjbull]

Actually, not sure that we need this PR if we merge #349. It may be nice to give folks a warning on this version, but since we can do side-by-side, people can simply upgrade to the next release if they need pydantic v2 support.