feat(django-spanner)!: support Django 5.2 and deprecate Django 3.2/4.2 (#16624)

This PR migrates the `django-google-spanner` package to support Django
5.2 and deprecates support for older Django versions (3.2 and 4.2). Due
to the deprecation of older versions, this is a breaking change and
requires a major version release.
**💥 BREAKING CHANGES**:
*   Dropped support for Django 3.2 and 4.2.
* Minimum supported Python version is now 3.10 (as required by Django
5.2).

Author: sinhasubham