Create a custom waiting room page preview

Creates a waiting room page preview. Upload a custom waiting room page for preview. You will receive a preview URL in the form `http://waitingrooms.dev/preview/`. You can use the following query parameters to change the state of the preview: 1. `force_queue`: Boolean indicating if all users will be queued in the waiting room and no one will be let into the origin website (also known as queueAll). 2. `queue_is_full`: Boolean indicating if the waiting room's queue is currently full and no...