feat: add redis sentinel support

Flask-redis https://github.com/underyx/flask-redis doesnt support redis+sentinel://, where redis-py support it.

Flask-redis doesn't seems supported, or no recent activity, I'm not sure if this will be easily upstreamable.

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Other redis protocol like the default, are still supported.

configuration.py
    'REDIS_URL': 'redis://redis:6379/0',

This allows to use non-supported by redis lib scheme redis+sentinel. Eg:

redis+sentinel://[:password@]host:port[,host2:port2,...][/service_name[/db]][?param1=value1[&param2=value=2&...]] rediss+sentinel://localhost:26379[,otherhost:26379,...]/mymaster/0

This prevents having several env vars but keep using just REDIS_URL.

Resources:

• https://github.com/exponea/redis-sentinel-url/blob/a91e6538a5362805b414fd14182883133ad9e594/redis_sentinel_url.py
• https://github.com/underyx/flask-redis