create proposal for upgrade16 to replace all priceFeed vats

[Chris-Hibbert]

What is the Problem Being Solved?

#8400 reported that the priceFeed vats hold onto old quotes in their recoverySet, preventing them from being collected. #9013 made recoverySets optional. #8740 showed how to update the priceFeeds and their clients. #9283 applied the fixes to master. We have recent results showing that after these fixes, priceFeed vats and Zoe no longer grow as price updates are submitted.

Description of the Design

The next step is to apply the fixes from #9283 to an upcoming upgrade. (currently planned to be upgrade 16) Mainnet has different price feed vats, so the proposal will be different.

Security Considerations

N/A

Scaling Considerations

This is all about remediating a known problem on the running chain.

Test Plan

The approach has already been tested. We'll need to verify the script in a testNet, which will have yet other different priceFeeds.

Upgrade Considerations

Yes