Support running Redis redundantly

Currently, we only support Redis's primary-replica mode. When the node that hosts the Redis primary goes down, applications break, as we can only read from the replica.

We should support running Redis redundantly. There are two approaches:

• Redis Cluster. Mostly meant for scale. Seems to be natively supported by Laravel.

• Redis Sentinel. Mostly meant for HA when not using Redis Cluster. It is not clear what the advantage of not using Redis Cluster is. Does not seem to be natively supported by Laravel.