Resolving an entity modifies OpenRosa hash and ETag of entities CSV

The entities CSV has an OpenRosa hash and ETag based on the latest `createdAt` or `updatedAt` among the entities. When the OpenRosa hash changes, OpenRosa clients will re-download the entities CSV. Right now, if an entity is marked as resolved, its `updatedAt` timestamp is changed even if no new version of the entity is created. That has the effect of changing the OpenRosa hash and ETag. I think it is the correct behavior to change the `updatedAt` timestamp in this way, as that's similar to what we do with submission review states. However, I think we should try to find a way to avoid the side effect of re-download to OpenRosa clients.

This issue seems thematically related: getodk/central-backend#1041. That said, the two issues might end up being pretty separate.