Add loggable model requirement to RailsApiLogger engine

[dpaluy]

After upgrading to v0.10 I got the following error: uninitialized constant RailsApiLogger::Loggable (NameError)

It means that the RailsApiLogger::Loggable module is being referenced before it’s loaded.

Zeitwerk manages the Rails autoloading mechanism, which doesn’t automatically load files from the app/models directory unless they’re explicitly referenced or used within the application.

This patch resolves this issue.