The KEYS command needs to be keyless

[Dltmd202]

The KEYS command needs to be keyless

The request policy of the KEYS command specifies that the command should have a request_policy:all_shards.

127.0.0.1:6379> COMMAND INFO KEYS
    1)  1) "keys"
    2) (integer) 2
    3) 1) readonly
    4) (integer) 0
    5) (integer) 0
    6) (integer) 0
    7) 1) @keyspace
       2) @read
       3) @slow
       4) @dangerous
    8) 1) "request_policy:all_shards"
       2) "nondeterministic_output_order"
    9) (empty array)
   10) (empty array)

As such the parameters of the command should be considered keyless and the routing should be done to all nodes. Right now we have a K key parameter, which would assume that we need it for routing.

The underlying logic does route (in multi-shard environments) the command to all shards, but it still treats the parameter as a key for the purposes of serialization.

This is somewhat invalid if a user configures their own codec, because it requires that they treat keys and patterns with the same abstraction.

Closes #3311

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[Dltmd202]

Hi @tishun, could you please take a look at this PR when you have a moment?