Adds new functionality on the backend that will merge any file from the
config directory that matches `<partName>.json` or `<partName>/*.json`
into the corresponding config part (presets, termthemes, etc.). This
lets us separate the AI presets into `presets/ai.json` so that we can
add a dropdown in the AI preset selector that will directly open the
file so a user can edit it more easily. Right now, this will create a
preview block in the layout, but in the future we can look into making
this block disconnected from the layout.
If you put AI presets in the regular presets.json file, it will still
work, since all the presets get merged. Same for any other config part.
