Fixture Manager should add new options to pre-existing config files

[thomasjthomasj]

Current you get a notification if running composer update and a new option is added to the config fixture, but I can't see any reason why it can't just edit the file and add the additional options to the end of the file, similar to how the installer amends the file

[kuiche]

Depends how deep you want to default. The tax config for example would break this if it defaults deeper than one level into the config file as there are configurations which would be removed by the dev and restored by this process.

Not all configs are simple k->v pairings.