[Feature] Export PGN as study chapter

[tom-anders]

Relevant API: https://lichess.org/api#tag/Studies/operation/apiStudyImportPGN

IMO this should be possible in the following places:

• Analysis board
• Over-the-board screen
• Post-game dialog (?)

The endpoint currently only supports adding to an existing study. So we should display a dialog that allows the user to select from their studies, and also to edit the PGN metadata and/or chapter name