Support Redis 7.0.0

[aarongable]

Version 7.0.0 of Redis was recently released, and contains a variety of backwards-incompatible changes.

One such example is that version 7.0.0 has extended the number of fields in the "CLUSTER SLOTS" command response, by adding a new "hostname" field. The current code in this library returns an error when it encounters such a response, since it expects only 2 or 3 elements (the IP, Port, and optionally the ID).

Please work towards support for Version 7.0.0 by resolving this and other incompatibilities.

[khasanovbi]

Also redis now return errors like ERR <message>, previously redis return just <message>.

[tomasgareau]

Thought I'd pop in here and leave a quick breadcrumb trail to redis/redis-py#1813 -- it's an issue tracking the Redis 7.0 features that the Python client needed to get in place and it has a great checklist of changes/new commands that might need to be supported.