API for uploading puzzles and studies

Just like Lichess has APIs for downloading puzzles, it would be helpful if we had an API for upload, so that:

- one can upload private puzzles or newly created puzzles.
- one can upload private studies or newly created studies.
- bulk upload all the PGNs containing the studies/puzzles.
- some mechanism to organize the uploads via API to arrange them in a logical order of chapters in the "study" or "puzzle group"

For example: In case of single uploads, we can pass a JSON in the body with the single upload "ids" or "lichess upload urls", puzzle names, chapter names, and the title of the study. The JSON structure would be used to group them into chapters and order the chapters into one study.
For bulk upload, we can have a similar implementation and pass the information on how to organize the data in a JSON.

Note: The upload file type would be in PGN or FEN

If something similar already exists or there is a workaround, please help me out with the same.

Start by reviewing the existing Lichess APIs for downloading puzzles and the repository's documentation and examples. Define the upload scope, including single and bulk PGN/FEN uploads, private content, and ordering puzzles or studies into chapters; done means the API behavior and organization model are specified and documented.

Written by the indexing model from the issue text.