Draft: Allow non-idempotent blocks in MultiStore pipeline

What does this MR do and why?

Changes the way we send commands in multi / pipeline commands so the block can be non-idempotent

How to set up and validate locally

1. Setup a different Redis db in config/redis.cluster_shared_state.yml
2. Enable use_primary_and_secondary_stores_for_shared_state feature flag

Test script:

nb = nil

::Gitlab::Redis::SharedState.with do |redis|
  redis.default_store.set('testkey', 100)
  redis.non_default_store.set('testkey', 0)
end

result = ::Gitlab::Redis::SharedState.with do |redis|
  redis.multi do |m|
    nb = m.incrbyfloat('testkey', 1000)
  end
end

puts result.first
puts nb.value

On master, it would return different values. On this branch, both will be the same.

MR acceptance checklist

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