Update redis backend support

[Nagico]

feat:

• native django redis-py, django-redis backend based on url connection: add USER field for authentication
• native django redis-py, django-redis backend based on socket connection: add USER and PASSWORD field for authentication
• django-redis-cache backend: throw exception when USER field is set
• test_redis.py file: replace pytest.mark.skipif with pytest.fixture and mock, add conftest.py file which provides django_cache_url_dj3 and django_cache_url_dj4, two mocked modules as fixtures, for each test function.

fix:

• native django redis-py backend: covert the keys in the OPTIONS to lower case
• uniform redis backends name:

# native django redis-py backend (Unchanged): 
BUILTIN_DJANGO_BACKEND = 'django.core.cache.backends.redis.RedisCache' 

# django-redis backend (Add a new variable)
DJANGO_REDIS_BACKEND = 'django_redis.cache.RedisCache'

# django-redis-cache (Unchanged): 
DJANGO_REDIS_CACHE_LIB_KEY = 'redis-cache'
DJANGO_REDIS_CACHE_BACKEND = 'redis_cache.RedisCache'

# default redis backend, depend on django version (Replace DJANGO_REDIS_BACKEND with DEFAULT_REDIS_BACKEND)
DEFAULT_REDIS_BACKEND = DJANGO_REDIS_BACKEND if VERSION[0] < 4 else BUILTIN_DJANGO_BACKEND

docs:

• readme.rst file: update redis, rediss, hiredis usage about authentication and native redis backend

---

More information about available schemes of different redis backends

• native redis backend in Django 4 and redis-py
• django-redis
• django-redis-cache

[epicserve]

Thank you for your contribution. I finally had some time to review this. I've added a couple of comments in the code.

[epicserve]

You don't need to install mock; you can use unittest.mock.

[epicserve]

It might be good to set VERSION[0] < 4 to a constant like:

IS_DJANGO_VERSION_GTE_4 = VERSION[0] >= 4

Then when parse() is called, add something like the following inside the function:

if IS_DJANGO_VERSION_GTE_4 is True and url.scheme in ('redis', 'rediss', 'hiredis'):
    warnings.warn(
        (
            "django-cache-url is no longer needed since Django version 4 or newer has a native Redids backend built in."
            "See the Django documentation (https://docs.djangoproject.com/en/4.0/topics/cache/#redis) for details."
        ),
        DeprecationWarning
    )