Support seeding confirmation

[Drarig29]

As said here: #59 (comment)

You can either use manager.create() for BYEs or manager.update.seeding() for TBDs.

But, as said here: #130 (reply in thread)

Once we need to start the tournament (because the registration phase is ended or whatever), TBDs are tricky because they are not actual BYEs so they are not propagated and do not make opponents automatically win.

So instead of letting the library user recreate the stage with the final seeding as a workaround, we could have a new function to the API:

• manager.update.confirmSeeding()

[Drarig29]

manager.update.confirmSeeding() was added in: https://github.com/Drarig29/brackets-manager.js/releases/tag/v1.4.2