Drop-in alternatives for Redis server to use the RedisEvalParallelSampler

[omsai]

Motivation/Application
This article in LWN points out that Redis will be released under non-free licenses from version 7.4 onward. From the abstract:

On March 21, Redis Ltd. announced that the Redis "in-memory data store" project would now be released under non-free, source-available licenses, starting with Redis 7.4. The news is unwelcome, but not entirely unexpected. What is unusual with this situation is the number of Redis alternatives to choose from; there are at least four options to choose as a replacement for those who wish to stay with free software, including a pre-existing fork called KeyDB and the Linux Foundation's newly-announced Valkey project. The question now is which one(s) Linux distributions, users, and providers will choose to take its place.

Currently, the documentation describes RedisEvalParallelSampler as the "most-used" and "best-supported" parallel sampler, so it makes sense to test and list Redis server alternatives. In case the Redis server alternatives are not as satisfactory then the parallel sampler suggestion(s) on the documentation page may need to be revised.