Add optional source parameters: generateId and promoteId (maybe others?)

[wfield-CUNY]

I was wondering if there's been any thought about adding a generateId checkbox for geojson sources or a promoteId for geojson or vector sources. I've been manually editing the style.json as needed but then the changes get overwritten by the editor. I added a generateId checkbox on my fork pretty easily but then when thinking about promoteId I realized some more thought had to be given before submitting a pull request.

What are peoples' thoughts on optional parameters? promoteId and generateId are mutually exclusive but also both optional so mainly I'm wondering what makes the most sense in terms of UI/UX

PS I'm loving maputnik and it's been a crucial part of my org's transition to FOSS!