Change Snowflake rendezvous to use Azure

Because of legacy/trac#25804 (moved), the App Engine–based rendezvous doesn't work anymore. In legacy/trac#22782 (moved), we set up CloudFront and Azure ones. However, because of recent messages from CloudFront, it's probably better to use Azure.

This rendezvous is also pointed at a different broker (the standalone broker from legacy/trac#22874 (moved)). But the change will not be noticeable to users. We actually meant to switch to the other broker earlier.

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information