Feature request: support default redis backend

[glasnt]

As of Django 4.0, there is now core support for the redis backend.

Currently, django-environ detects uses package inspection to work out which redis backend to use (in environ/compat.py), which uses redis_cache if detected, or it defaults to django_redis.

I think this package should default to using the core backend if using Django 4.0 or above/

(I am working on this in a branch on my fork. Pull Request shortly.)

[glasnt]

TIL while writing tests that Env.cache_url_config exists, and so there is a workaround for now (which I couldn't find any explicit documentation for:

CACHES = {
    'default': env.cache_url('REDIS_URL', backend='django.core.cache.backends.redis.RedisCache')
}

Also looking through the tests, I realise supporting Django 4 is not something this package currently does, and there would be copious test changes to ensure Django 4 support in the first place.

For reference, here is the base code I suggest. This based on the logic that it should detect for a package before detecting for a Django version, being installing a package is an active choice on the user's part.

# environ/compat.py

# back compatibility with redis_cache package
if find_loader('redis_cache'):
    REDIS_DRIVER = 'redis_cache.RedisCache'
# default to built-in redis backend if available
elif DJANGO_VERSION is not None and DJANGO_VERSION < (4, 0):
    REDIS_DRIVER='django.core.cache.backends.redis.RedisCache'
else:
    REDIS_DRIVER = 'django_redis.cache.RedisCache'

[glasnt]

It may also make sense to use a new scheme for the core redis, much like how there's memcache and pymemcache. That should help more with backwards compat.

[xblitz]

good job, any chance to create a Pull-Request for this?

[sergeyklay]

Implemented in #397. Thank you for contributing!