Re-Add PING connection command

[DiogoLAzores]

During #825, the PING command, alongside other connection commands, was removed since it was considered useless.

At the moment, said command would be useful for my company's health endpoints, as it can attest the healthy communication of each API with Redis.

Since there was no explicit reason for those commands to be removed, would this topic be pertinent? Why was PING removed?

Thanks in advance for you time!

[mijicd]

Sorry for the delayed answer. It was likely among the "rarely found" commands in some other clients. I don't mind reintroducing it. If you have cycles feel free to submit a PR, otherwise we will tackle it.