timing work-around for stATOM proposal

[turadg]

What is the Problem Being Solved?

@0xpatrickdev made an add-stATOM proposal. We've since uncovered some timing gotchas, noted in #8177 (comment)

Description of the Design

Adapt the proposal logic in #8177 that works around the timing problem and submit to https://github.com/0xpatrickdev/agoric-vault-collateral-proposal/ for consideration in the Mainnet proposal

includes adding code to handle timing constraints to avoid #8296, #8307
per meeting with @turadg and co

Without a fix, it's crucial that the oracle be started before the auction, and that the new brand is added to the auction after an auction round ends and before the next one starts.

Security Considerations

Scaling Considerations

Test Plan

Upgrade Considerations