Detailed Description

Add user-editable metada for datasets and folders.

• The metadata should be in the form of Dict<str, str | int | Array<str>>.
• The existing dataset.details can be reused for this.
• Dataset tags should move into this metadata structure as "tag": Array<str> key-value pair.

This needs to be implemented in backend and frontend. We'll probably need a migration to migrate the tags. In the frontend there should be a key-value editor for datasets (in dataset settings) and folders (in the edit modal).

The API should also be exposed to be used in the wklibs to read/write metadata.