Make Snowflake's DTLS fingerprint more similar to popular WebRTC implementations

Some recent work by researchers at Princeton shows that Snowflake's DTLS fingerprint differs from some other popular WebRTC implementations (Facebook, Google, and Discord): https://arxiv.org/pdf/2008.03254.pdf

I'm hesitant to rush changes to the fingerprint without a more complete comparison to more WebRTC implementations popular in censored regions. But, we can get a start on figuring out how to change the fingerprint in pion and see whether we will need to submit upstream patches to provide us with this kind of agility. Something like uTLS would be great for us in the long run.