JoinStrategy: "auto" | "manual" | "disabled"

The join strategy, represented by a value from the following list:
- 'auto' : The player will automatically join a cast session if one exists when play is called. Otherwise it will prompt the user with all available devices.
- 'manual' : The player will take over an existing session if there is one and the cast button is clicked. Otherwise it will prompt the user with all available devices.
- 'disabled' : The player is not affected by cast sessions and is not castable.