Add an upload SGF field to the player challenge modal

[runarberg]

Is your feature request related to a problem? Please describe.
I am a maintainer of a website that generates an SGF with a random starting position. I find the UX of starting a game from a generated position a little cumbersome:

1. Uploading the downloaded SGF to my SGF library
2. Open the uploaded SGF
3. Fork the game
4. Challenge a player

This is quite un-intuitive and hard for users to discover on their own. This applies both to starting positions generated from my website (or others like it) and in general when users want to continue from an SGF they found somewhere

Describe the solution you'd like
It would be neat if we could simply upload the SGF straight to the modal.

This way a user wouldn’t need to bother with the SGF library at all for one off game challenges. Even better if users could drag and drop SGF data into the field. That way SGF generating websites could simply implement a drag behavior that carries the data, and when it is dropped to the field OGS knows that the game should start from it. No need to even download the SGF file even.

Describe alternatives you've considered
We could simply keep things the way they are. It isn’t terrible, just a little un-intuitive and cumbersome (i.e. many steps).

[github-actions]

This issue has been marked stale and will be closed soon without further activity. To keep the issue open, please respond to the comment to keep the discussion going.

[github-actions]

This issue has been automatically closed due to inactivity. Please feel free to re-open it if the issue persists.