Add Django-4.2 support

[shimizukawa]

Django 4.2: April 2023 https://docs.djangoproject.com/en/dev/releases/4.2/

• update tox and github CI
• update pyproject.toml
• update document
• bump version x.Y.z for imcompatible update

Important

• Psycopg 3 support
• Comments on columns and tables
• Dropped support for PostgreSQL 11
  • Upstream support for PostgreSQL 11 ends in November 2023. Django 4.2 supports PostgreSQL 12 and higher.

[shimizukawa]

• Psycopg 3 support

Psycopg3has been supported since Django 4.2.
https://docs.djangoproject.com/en/4.2/releases/4.2/#psycopg-3-support

Redshift is forked from an older version of Postgres, and the Django database backend for Postgres that can be used for Redshift is only available up to Django 4.0.
For the support of Django 4.2 this time, django-redshift-backend includes the database releated code from Django 4.0.
Therefore, Psycopg3 could not be used.