FI-956: Add Generated Sequence to config.yml

[radamson]

This PR updates the generate rake task to automatically append the generated module to the configuration. An optional argument allows the user to prevent this from happening.

A ConfigManager class was added to help manage loading, updating and writing the config. I'm not sure if we'll want to use this in more places in the future (instead of App::Endpoint::settings and I figure that may be best left for a future PR as the real goal here is to update the generate task.

Note: Adding the newly generated module to the config will remove and comments in an overwritten yaml file

[arscan]

We discussed other options that avoid editing config.yml (having a script editing a human-editable config file seems like an anti-pattern), but this works for now and we can look to refactor in the future.