Evolutions remove `notBefore` from bindings

[psFried]

Steps:

• Start with a materialization where one of the bindings specifies notBefore
• publish an incompatible change via the UI
• Click "Apply recommended actions" to increment the backfill counter
• Drafted materialization binding is now missing notBefore

We should check to see if anything else is getting cleared out accidentally, too. This issue can certainly be resolved as part of the re-framing of evolutions as part of controllers. But we can probably also fix it sooner if there were urgent need.

[psFried]

I looked at the evolutions code in agent and found that it's cloning the entire binding and then just incrementing the backfill counter. I really don't see how it could be removing notBefore or anything else. So I decided to try performing an evolution manually by creating a draft and inserting a row into the evolutions table. When I did that, it preserved all the notBefore fields as expected. So now I'm thinking perhaps the UI is involved.