Migration process is rather ad hoc and needs one off integrations

[thoughtpolice]

The migration testing tool migration-test mostly just makes sure that the binary tables can be upgraded in place and that the schemas are compatible with pg_dumpall as a method. This isn't tested in the CI, and it's hard to think of how it should work. Notably, the migration tool is in some sense a tool for both regressions but also a tool for proactively finding and diagnosing issues.

It's unclear what a fully fleshed out tool would look like, especially since some migrations are probably "once in a lifetime events"; e.g. it would be rare for a migration to probably fail exactly the same way twice, so the use of writing really deep tests isn't clear. Instead, just having a way of automating the existing methods might be enough.

This is likely something that will just need some experimenting to find the right balance.