Support HTTP/2 End-to-End (To the Dyno)

In May of 2024, Heroku [released the public beta](https://blog.heroku.com/heroku-http2-public-beta) for HTTP/2 on Heroku, with HTTP/2 terminated at the router and HTTP/1.1 forwarded to the dyno. We would like to support the HTTP/2 protocol end-to-end to unlock features like Server Push and gRPC services. This requires TLS termination done at the dyno level, and more research is needed regarding certificate management at the dyno level to support this.

Further customer feedback regarding end-to-end use cases from the original [HTTP/2 roadmap item](https://github.com/heroku/roadmap/issues/34) can be found below:

https://github.com/heroku/roadmap/issues/34#issuecomment-1500960951
https://github.com/heroku/roadmap/issues/34#issuecomment-1515400507
https://github.com/heroku/roadmap/issues/34#issuecomment-1560496404
https://github.com/heroku/roadmap/issues/34#issuecomment-1666577157
https://github.com/heroku/roadmap/issues/34#issuecomment-2091092821
https://github.com/heroku/roadmap/issues/34#issuecomment-2099174917