Update pydantic to support v2

[francbartoli]

Overview

Related Issue / discussion

See:

• Compatibility with Pydantic >= 2 through pydantic.v1 #1664
• validate pydantic version when testing on Debian #1766

Additional information

Dependency policy (RFC2)

• I have ensured that this PR meets RFC2 requirements

Updates to public demo

• I have ensured that breaking changes to the pygeoapi master demo server have been addressed
  • https://github.com/geopython/demo.pygeoapi.io/blob/master/services/pygeoapi_master/local.config.yml

Contributions and licensing

(as per https://github.com/geopython/pygeoapi/blob/master/CONTRIBUTING.md#contributions-and-licensing)

• I'd like to contribute [feature X|bugfix Y|docs|something else] to pygeoapi. I confirm that my contributions to pygeoapi will be compatible with the pygeoapi license guidelines at the time of contribution
• I have already previously agreed to the pygeoapi Contributions and Licensing Guidelines

[webb-ben]

Support general housekeep but seems like this PR should just include the changes made in pygeoapi/models/config.py, pygeoapi/models/openapi.py, requirements-django.txt, and requirements.txt.

Note: because we are using Ubuntu Noble for the Dockerfile, it might be worth coming to a quorum about what version of Ubuntu pygeoapi is supporting. If we want to be in line with RFC2, wouldn't we want to downgrade the Dockerfile base image? If we want to keep it on Jammy, I would also recommend including python3-pydantic in ADD_DEB_PACKAGES

[tomkralidis]

Pending discussion in #1766

[kalxas]

CI fails.
@francbartoli can you please rebase only the core pydantic commit (0a03614) to master?

[kalxas]

Thanks for fixing CI.

[kalxas]

Please do not squash when merging. I would like to keep the core pydantic 2 commit in git history

[francbartoli]

Should I merge or wait for another approval?

[tomkralidis]

Given we are releasing 0.20.0, I would prefer to merge this immediately after 0.20.0 is released (at which point we will create a 0.20 branch).