persist: update postgres consensus to page through versions

[pH14]

Quick PR to put some bounds on the scan query and page through the resultset. If gc ever falls behind, we should be polite to CRDB and not ask for unbounded amounts of data at once.

Motivation

• This PR fixes a previously unreported bug.

Tips for reviewer

Checklist

• [x] This PR has adequate test coverage / QA involvement has been duly considered.

• [x] This PR evolves an existing $T ⇔ Proto$T mapping (possibly in a backwards-incompatible way) and therefore is tagged with a T-protobuf label.

• [x] This PR includes the following user-facing behavior changes:

  • N/A