Enable Redis compression of keys

We have a lot of Redis keys that store uncompressed, large text blobs. The Redis cache store has support for key compression (https://api.rubyonrails.org/classes/ActiveSupport/Cache/RedisCacheStore.html#method-c-new). We've turned it off here: https://gitlab.com/gitlab-org/gitlab-ee/blob/cfe4caaff3b7aa36c95e295180d1dc007bb6efab/config/application.rb#L257

To reduce the payload size and network bandwidth, we may want to consider turning this on, at least for a subset of keys to start. This might add some CPU load on the Web application servers, but it ought to help the Redis server.

/cc: @Alexand