Pass watch: kwarg to #multi calls on clients

[KJTsanaktsidis]

Both RedisClient and RedisClient::Cluster have #multi methods that accept a watch: kwarg to watch keys as part of the transaction. See:

• https://github.com/redis-rb/redis-client/blob/ba8848b195404ab337daa94647f600b1a4506f0f/lib/redis_client.rb#L419
• https://github.com/redis-rb/redis-cluster-client/blob/c00ee01d087471b690f44ecbac8d0cea005783fd/lib/redis_client/cluster/transaction.rb#L36

However, the subclasses Redis::Client and Redis::Cluster::Client in this gem(s) don't forward these keyword arguments, so you can't take advantage of them.

This PR simply delegates the watch argument.

[byroot]

Yeah, I guess it's a nice shortcut.

[KJTsanaktsidis]

That's got to be the fastest merge I've ever had! thanks.

Yeah, I guess it's a nice shortcut.

It's actually a little more important than a shortcut for cluster mode - the watch/unwatch machinery in Redis::Commands::Transactions doesn't work properly with redis-cluster-client because it doesn't store transaction-related state (like what slot we have to ensure everything is in) outside of a call to #multi. So this pattern doesn't work.

$redis.watch('{hash}key1', '{hash}key2') do
    $redis.get('{hash}key1')
    # oops, don't like what I read out of key1, let's not do the transaction after all.
    $redis.unwatch
end

Using the multi(watch: ...) pattern does work though (once redis-rb/redis-cluster-client#294 gets merged).

I do want to make Redis::Cluster#watch do ... end work properly though if possible, I think that needs a little more surgery though so starting with this seemed easier.