Improve demo Zaps

[rebeccacremona]

• post a response back right away, so you can tell it worked
• with the WACZ, include a message that reminds people they need to download before whatever time, and/or if possible send the actual file to Slack
• with the WACZ, include a "preview" playback link like https://replayweb.page/?source=https%3A%2F%2Fpermafact.s3.amazonaws.com%2Fprod%2F47e68bc5-c58f-4182-939a-b85e9f330cfe.wacz%3Fresponse-content-disposition%3Dattachment%253B%2520filename%253Dwww.youtube.com-2021-02-02.wacz%26AWSAccessKeyId%3DAKIA5KOZV3IM3QJ6LY4W%26Signature%3DRBl6d0vnsl7sDAY7RLqXtKTgqFA%253D%26Expires%3D1612297495%26.wacz#view=pages&url=https%3A%2F%2Fwww.youtube.com%2Fwatch%3Fv%3DNPqfoAhIzJM&ts=20210202172336. Note that the validation evidently wants the URL to end in .wacz, so you have to add &.wacz to the source URL after the other GET params... at least if you use the form. I didn't check what happens if you just remove the extra param from the above.

[rebeccacremona]

Also, the zaps will need tweaking for the new API.

Also, our ability to publicly share zaps have changed, so we might not be able to distribute these as intended. Look into the best way to share.