Enable native Redis cluster

[jaketlarson]

Summary

There seems to be work done already on migrating to native Redis clusters. I set up a cluster locally to test but could not compile because it seems that it's manually disabled until we rename redis_clusters to clusters in utils/redis.py:
f41ecd3#diff-eca64da2111d6c6353c9e16283daac43R125

Motivation

I'm not sure what missing pieces are left before migrating to redis clusters, but we are looking for some form of persistence via the master/replica paradigm, and from what I've gathered, the Redis Blaster setup Sentry currently uses does not support that. If a node in the Redis Blaster cluster goes down, it seems like we'd lose the data entirely with connection errors thrown.

[semistone222]

I also want to use redis cluster (master/replica).

[BYK]

@wedamija @mattrobenolt @joshuarli do you know we already have this now?

[joshuarli]

Transitioning the remaining redis-blaster-based clusters to redis-cluster-based is desirable, but I don't see that happening in the short term. At least, I recently briefly attempted it for TSDB, but struggled with some rb -> rc API conversions and moved on to other things.

[mattrobenolt]

Yeah, this is very nontrivial to do and haven't had much motivation to do the work yet. We will eventually. But it hasn't been important enough for us yet.

[ilya-jetruby]

Still actual