Add initial support for FRRouting

[soymgomez]

I add a first functional version to integrate FRRouting and to be able to export its configuration.

The model is based on the Cumulus model but I use directly vtysh to export the running config.

I know it can be improved but at least I have it as a base to improve it in the future.

Pre-Request Checklist

• [ ] Passes rubocop code analysis (try rubocop --auto-correct)
• [ ] Tests added or adapted (try rake test)
• [ ] Changes are reflected in the documentation
• [ ] User-visible changes appended to CHANGELOG.md

Description

[mortzu]

Please add to CHANGELOG.md and to documentation (supported devices)