[Bug] Redis connection loss resiliency

[Vince-Chenal]

Is your feature request related to a problem? Please describe.

• CHProxy won't startup if one of the defined redis cache is not reachable.
• When redis cache is down CHProxy is taking a lot of time to answer requests (probably waiting for a timeout from redis connection).

Describe the solution you'd like
We could make CHProxy resilient to Redis connection loss