Public open studies

[WandererXII]

          I have another suggestion related to this issue. I think it would be nice to have an option to just create a public study where everyone who spectates the game or has a link to the study can participate. I feel like in most cases most people don't expect bad actors to hop in on their studies and cause problems. I'm not quite sure how difficult could it be to implement, but it sounds like a very easy to understand and useful study option under the "+" button.

Originally posted by @Anfid in https://github.com/WandererXII/lishogi/issues/657#issuecomment-1519039460