Metadata editing improvements

[silvester-pari]

• add way to input geographic data for products (map + text input as alternative)
• add markdown info and preview for description fields
• error handling & error message display in forms
• move OSC-backend endpoint url to centralized config
• adjust request body format for projects & products to fit STAC requirements
• review which fields can be edited (e.g. unique ID should not be editable)
• introduce way to DELETE an item
• add field to add WMS link for products
• BACKEND: pass authenticated user parameters (email/github handle) to requests for backend to use
• BACKEND: add line breaks for generated json files
• BACKEND: retrieve PR metadata (type like new item, edit item ect., plus link to PR)
• BACKEND: retrieving pending items - only retrieve items by user who does request
• BACKEND: add special label to PRs from "data owners"