Target Redis server version

[lewispb]

While working on a feature recently I was exploring the use of the ZADD options GT and LT. These are only available in Redis 6.2 onwards.

Do we have a minimum Redis server version in mind while developing Kredis? If not, can we document one?

The only reference to a version I could see was this line: https://github.com/rails/kredis/blob/main/lib/kredis/migration.rb#L8

[dhh]

I believe we're at Redis 4+ at the moment since that's what Rails suggest in the default Gemfile.

But we probably could just gate new features on a redis version check? Then fail if not available?

[lewispb]

Added a note to the readme in #79.

I backed away from GT / LT so nothing in mind that would require gating right now, but good to know that's an option for the future.

Might be worth also adding a matrix of supported Redis server versions, say 4 and 6.2, and client libraries to CI?