Manage configuration in plain text

Currently, ESAP API configuration is all stored in SQLite databases.

Among other things, that causes us to have pretty impenetrable MRs like esap-api-gateway!100, which replaced one opaque blob with another. It's hard to review when you have to download the database and poke at it with command line tools to see what changed.

A better solution would be to version this configuration in plain text (probably YAML, but whatever), then use that as fixtures to prime the database at build time.