Per project configuration that extends from the home config

[antran22]

Occasionally I need to define a custom fence configuration for a project. Currently the flow would be:

• Copy $HOME/.config/fence/fence.json / ~/Library/Application Support/fence/fence.json to the project directory (fence.json for example)
• Make additional modification
• Refer to it: fence --settings ./fence.json

I think it would be a clean DX if in case of no explicit --settings flag, the app would:

• Implicitly lookup a fence.json file up the directory tree
• When we find one such file, consider making it extending from the base config, then use that config
• When no fence.json file is found, use base config file.