Diagnostic Support for Adding Migrations

[MavenRain]

Currently, if you add a new migration to ledger_migrations.json, and the name entry of that migration does not exactly match the name entry in the migration code, e2e migration and staging tests fail with a vague "Unsupported migration". Ideally, the name of the unsupported migration should be added to the error message, along with all of the migrations that are supported, so that the developer previously unfamiliar with the migration framework can spot the difference, particularly if it is a simple typo.