Add support for loading config in config file

[ccremer]

Summary

• Adds global flag --config / -C to a path of a config file
• Makes many flags loadable from the config file (not all though)
• Adds a init subcommand to prepare a new config file
• Run init - to display the list of options that are configurable in the YAML file, or run init to create a new config file.

Checklist

• Categorize the PR by setting a good title and adding one of the labels:
  kind:bug, kind:enhancement, kind:documentation, kind:change, kind:breaking, kind:dependency
  as they show up in the changelog
• Link this PR to related issues