Augment quic interop harness to support server side interop tests

Augment quic interop harness to support server side interop tests

the quic-interop-runner that we use for interop testing currently only
supports openssl client testing, as we had previously not had a server
to test with.

This PR rectifies that by doing the following:
1) Adding a quic-hq-interop-server.c file in demos/guide
2) Augmenting our interop Dockerfile and entrypoint to support our
   interop containter running in a server role

With these changes we are able to do server side interop testing

Reviewed-by: Saša Nedvědický <sashan@openssl.org>
Reviewed-by: Tim Hudson <tjh@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/26000)