Add external datasources for select fields

I would like to add external datasources for select fields. I will use a sql database in addition to caisy, and I have some serverless functions returning a list of entries as an array of json objects. (e.g. mypage.com/api/v1/categories) will return an array of objects like [{value: 'mycategory', label: 'My category'}, ...]

I would like to have a possibility to add this endpoint to my select fields as possible values, so that an author can select one of these entries.