feat: allow setting Redis connection options

[alexei]

redis.from_url may accept connection options specified as kwargs. They're not particularly documented, but a list may be found in the source code:

URL_QUERY_ARGUMENT_PARSERS = {
    'db': int,
    'socket_timeout': float,
    'socket_connect_timeout': float,
    'socket_keepalive': to_bool,
    'retry_on_timeout': to_bool,
    'max_connections': int,
    'health_check_interval': int,
    'ssl_check_hostname': to_bool,
}

I think most people don't need them and django-health-check works fine with the defaults.

That said, there is one particular case which I think django-health-check needs to deal with which is e.g. Heroku uses self signed certificates which causes the connection to fail (raising a ConnectionError) which in turn makes the Redis health check to report the service as unavailable. The issue can be worked around by disabling SSL verification. In order to do that, one needs to pass ssl_cert_reqs=None to the connection object.

This PR introduces a new variable HEALTHCHECK_REDIS_URL_OPTIONS which allows one to customise the connection if they need to.

[brockhaywood]

+1

[onlinejudge95]

@KristianOellegaard can we allow this, we use Redis with SSL in our cluster and our Django startupProbe are failing due to this

[BoPeng]

Ditto. Our healthcheck also fails to connect to rediss://.