Add scatter-gather

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What I Did

I would like to query all shards. This is expensive, but we need to do this sometimes.

What I See

I get a shard key not found error.

What I Expect

I expect a select query to be sent to all the shards and the results returned. I would add /* hint-allow-scatter-gather */ to the query text to indicate that the programmer knows that the query is expensive.

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In some discussions, it seems this may be too powerful and could be abused. Maybe thinking through a global-secondary-index case--possibly with caching--would constrain scatter-gather usage and keep hera sharding scalable.

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We think scatter-gather will cause too many scaling issues and abuse