Add Support for SPKI Pinning

[sumitsharansatsangi]

I was trying to run the following example . It works fine.

Now, for extra security, I want to pin public key of the server certificate on the client side and use it in the code, but I was unable to do.
If it is not possible yet, please add this functionality, if already implemented , then guide me how to do this

[boquan-fang]

S2N-QUIC delegates TLS configurations to the TLS layer. You will need to configure cert pining in the TLS provider.

For example, Rustls allows pining through rustls_pin crate.