feature: Direct Reservation context manager

[mbeach-aws]

Issue #, if available:

Description of changes: a new context manger to modify AwsQuantumTasks created within this context to run on a device with a reservation ARN.This is useful for ensuring that all quantum task

    Examples:
        As a context manager
        >>> with DirectReservation(device_arn, reservation_arn="<my_reservation_arn>"):
        ...     task1 = device.run(circuit, shots)
        ...     task2 = device.run(circuit, shots)

        or start the reservation
        >>> DirectReservation(device_arn, reservation_arn="<my_reservation_arn>").start()
        ... task1 = device.run(circuit, shots)
        ... task2 = device.run(circuit, shots)

Testing done:

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Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 100.00%. Comparing base (07d9e1e) to head (561c503).

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[kshitijc]

Context managers are typically used to allocate and release resources. If in the future we allow programmatic creation of reservations, will the proposed interface here make it hard to do that? Do we need to add in the context manager interface right now?

[speller26]

The use case for reservations is booking a slot ahead of time, with enough room for cancellation if needed; creation of a reservation upon entering the context manager could be a very long blocking call. As well, the current implementation doesn't rule out the world where reservation creation gets fast and fine-grained enough that one could reserve a device for immediate use; the reservation_arn field could become optional, with extra optional parameters added for creation.