Introduce ravioli gem to CDot project

Problem

The Ravioli gem provides a unified PORO approach to access Rails credentials, env variables without having to worry about defining overrides as such.

It also allows the ability to categorize configurations into separate file. More details on the features can be read on the gem page.

The use of ravioli gem for CDot application was suggested during the evaluation of this epic, as it fits well for the use case in the application: fetch a config from .env if present and default to Rails credentials if not present.

Proposal

Add the gem to the Gemfile as part of this issue.