Add support for SMISMEMBER command added in redis 6.2.0

[ported-pw]

Pull Request check-list

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• Does $ tox pass with this change (including linting)?
• Does travis tests pass with this change (enable it first in your forked repo and wait for the travis build to finish)?
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Description of change

• Add support for the SMISMEMBER command added in Redis 6.2.0 as mentioned in Redis 6.2 New Commands Check List #1434.
• Bump the server version used in the Docker test environment to 6.2.0 to test the new command
• Add support for the channels (new in 6.2.0) setting in acl_getuser and fix ACL tests using a version check to make them pass on 6.2.0. This does NOT add support for the channel ACLs in acl_setuser or support for it in general.

[ported-pw]

Some open questions:

• Is it actually a good idea to fix things related to 6.2.0 in this PR to make tests pass or should the tests rather fail so this PR only includes the commit for the SMISMEMBER command?
• Should I actually convert the returned integers to booleans or leave them as integers, more closely matching the redis documentation? What is the philosophy here, how much should we change about the returned data?
• Is it a good idea to use string_keys_to_dict even though it only adds one command? The thought here was that an Array of "Boolean" replies would be something that could be used elsewhere too.

Also, the CI failed because of
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[ported-pw]

Like mentioned in #1460 (comment), an unrelated unit test is failing on Redis 6.2.3.

[chayim]

Like mentioned in #1460 (comment), an unrelated unit test is failing on Redis 6.2.3.

IMHO I think this PR should just focus on the command being implemented. I'm a big fan of not bundling unrelated changes. Any chance you'd like to merge master in, and we can possibly get this in for the upcoming release? WDYT?

[chayim]

SMISMEMBER support itself is superseded by #1667 which separates out just the initial change for the command itslef.