migrator: Add `upgrade` command
Created by: efritz
This PR adds an sg migration upgrade
and migrator upgrade
command that runs the multi-version upgrade process as described in RFC 697: Multiple version upgrades.
Fixes #38048 (closed) (with reduced scope). Complete fix blocked by #38094 (closed) but tracked in #39578 (closed). This PR was supported by #39457, #39458, #39459, #39473, #39474, #39540, #39541, #39542, #39543, #39545, #39546, and #39553.
Test plan
Tested by hand locally. Added additional unit tests.