Add runtime schema validation support to diesel

[spencewenski]

Diesel and SeaORM both have their own tooling for running migrations, and Diesel's specifically will detect any changes between what's in the actual db and what's in the generated schema file (diesel migration run --locked-schema). This kind of thing isn't checked when we run migrations automatically in Roadster via the direct migration trait APIs.

We might want to consider removing the auto-migrations and instead recommend that migrations are run via each ORM's official tooling. TBD if there's any existing advice from Diesel or SeaORM on this topic.

[spencewenski]

It seems like at least diesel doesn’t discourage running migrations in the app. And it shouldn’t be too hard to add the schema verification for this approach: diesel-rs/diesel#4399