dev: resolve circular dependency in make db-schema target

[mastercactapus]

Description:
This PR aims to fix the pain with the make db-schema target.

Currently, it depends on building several dev tools, which also have dependencies on other parts of the app, that in turn depend on sqlc-generated code. Since all the application-related code in turn depends on the output of make db-schema this created a circular dependency that was hard to resolve.

This is made better by this PR by doing the following:

• psql-lite a dev-only tool, now has it's own sqlc.yaml file and can be built independently
• The make db-schema target now uses go run directly to further distance itself from build deps
• The SplitQuery helper was moved to util/sqlutil instead of requiring the entire harness
• psql-lite will now output the results of a select query, eliminating the dependency on psql itself
• A goalert-migrate command was added to allow applying migrations without building the full app

Going forward, if a merge conflict breaks migrate/schema.sql, devs can simply run make db-schema to regenerate it, similar to other generated files.

Additional Context
To validate:

• try deleting migrate/schema.sql and see that make db-schema still works
• try adding invalid syntax into migrate/schema.sql (e.g., merge conflict) and see that make db-schema still works