allow auction Bids to specify "exit on partial satisfaction"

[Chris-Hibbert]

What is the Problem Being Solved?

Individual bids in the Dutch Auction (#7000) should be able to specify that their seat in the auction should be exited after successfully bidding on assets, regardless of whether they were entirely consumed. This provides support for arbitrageurs whose goal in the auction is to immediately sell the proceeds at the current market price in order to take advantage of the discount they got in the purchase.

This is in contrast with bidders whose goal is to accumulate assets at a discount, and who therefore want to let their bid ride and be applied to future rounds. (Those bidders can have an onDemand exit condition and pull assets out occasionally.)

Description of the Design

This would be another field in offerArgs when exercising the invitation.

Security Considerations

This fits within the Zoe security architecture, and is well within the ability of a contract to carry out.

Scaling Considerations

No impact.

Test Plan

Nothing outlandish.