Update contour.yml config file to match actually existing keys

[Marenz]

Through constant updates, config files become out-dated and start missing keys or contain keys that have been removed or renamed.

This issue is about providing a way to auto-fix those keys, either automatically or by specific user request..

[Yaraslaut]

We wanted to make it happen at some point, the issue with that is that at the moment yaml-cpp API does not allow user to write comments to the files, meaning that if we try to update config file of the user it will delete all comments in the file. Maybe @christianparpart have some ideas about that

[Yaraslaut]

Will be implemented as part of https://github.com/contour-terminal/contour/issues/1282