feat: Add support for Python 3.12 (#223)

* chore(python): Add Python 3.12

Source-Link: googleapis/synthtool@af16e6d
Post-Processor: gcr.io/cloud-devrel-public-resources/owlbot-python:latest@sha256:bacc3af03bff793a03add584537b36b5644342931ad989e3ba1171d3bd5399f5

* add constraints file for python 3.12

* remove constraints file for python 3.6

* Add trove classifiers for python 3.11 / 3.12

* update prerelease and compliance workflows to use python 3.12

---------

Co-authored-by: Owl Bot <gcf-owl-bot[bot]@users.noreply.github.com>
Co-authored-by: Anthonios Partheniou <partheniou@google.com>

Author: gcf-owl-bot[bot]

bigquery/python-db-dtypes-pandas/snippets/noxfile.py

@@ -89,7 +89,7 @@ def get_pytest_env_vars() -> Dict[str, str]:
 
 # DO NOT EDIT - automatically generated.
 # All versions used to test samples.
-ALL_VERSIONS = ["3.7", "3.8", "3.9", "3.10", "3.11"]
+ALL_VERSIONS = ["3.7", "3.8", "3.9", "3.10", "3.11", "3.12"]
 
 # Any default versions that should be ignored.
 IGNORED_VERSIONS = TEST_CONFIG["ignored_versions"]