Provide an option to disable certain risky Redis commands

As discussed in https://redis.io/topics/security, it is considered good practice to rename or remove certain commands from a Redis cluster.

This should be done for security reasons, but also for availability.

For example, if an application developer accidentally delivers a change which issues a KEYS command, or if the KEYS command is issued from a rogue script, it could bring down the Redis cluster.

There are recorded incidents of this happening on GitLab in the past.

This can be prevented to renaming the command to a random hex string which is then kept secret.

We should allow this option, of renaming KEYS in Redis. It would be better if we did this by default, using a randomly generated string.

cc @estrike