Docs: Replace swaggerv2doc directive with openapi

Docs: Replace swaggerv2doc directive with openapi

Replace deprecated swaggerv2doc directive in PRH.rst with the openapi
directive from sphinxcontrib-openapi. The swaggerv2doc extension has been
removed from conf.py and requirements-docs.txt.

Modernise docs build configuration:
- Remove OpenStack Yoga constraints (conflicted with ONAP constraints)
- Update basepython from 3.8 to 3.12
- Add setuptools>=65.0.0 as explicit dependency
- Update .readthedocs.yaml to ubuntu-24.04 and python 3.12
- Align requirements-docs.txt versions with doc repo standards

Issue-ID: CIMAN-33
Change-Id: If39049c0403839b19f786283b2f7ff8ef2131485
Signed-off-by: Matthew Watkins <mwatkins@linuxfoundation.org>