WIP Swag at queueing requestors with an external api

Take member queuing:

There are two new options to configure a pool:
queue_max: Maximum depth of the requestor que
queue_timeout: The default timeout for a pool. This value can be overridden at runtime vi pooler:take_member_queued/3


Semantics are as follows
pooler:take_member_queued makes a blocking request to pooler. The timeout can be 
take_member/1 is an alias to take_member_queued/2 with the timeout set to zero

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