deprecating Twitter protocol in Thrift Proxy

[Raul Gutierrez Segales]

Hi all,

We’ve decided to deprecate support for Twitter (finagle) protocol in Envoy’s Thrift Proxy given that it's not used and it's causing significant maintenance burden.

So here’s the plan:

* this PR marks the Twitter Thrift protocol as deprecated in the config API

* we’ll also some extra warnings for when the protocol gets automatically detected
* around April of 2023, we’ll remove support for the Twitter Thrift protocol

If there’s any concerns around this, please reach out so we can work out the details.

More info on this change: https://github.com/envoyproxy/envoy/issues/20466.

Thanks,
-rgs