Add querystring parameters to limit which fields are returned

[Mr0grog]

For clients who don’t need detailed data, cutting some fields (e.g. availability.slots or availability.capacity) from responses can make the response smaller and make the queries faster since joins take less memory. We should add a querystring parameter than allows clients to ask for fewer fields.

I’m not 100% sure on the best form for this; it could be as simple as some presets, like ?detail_level=light, or it could be a comma-separated list of fields, like ?fields=id,external_ids,name,availability.valid_at,availability.available,availability.products.

This is not yet a high priority need, but I’m noting it down since Vaccinate the States wants to integrate on the front-end instead of the back-end, and this could be a particularly useful feature for that.

[Mr0grog]

This project has been shut down. This issue has been left open as a guide for anyone forking this project — addressing this issue (or at least knowing about it!) is likely to be worthwhile for you if you are maintaining a running copy or fork of UNIVAF.