[cluster-local-domain-tls] host cluster-local certificates with SNI in net-contour

[ReToCode]

Context

Vision: #14213.

Each net-* implementation needs to grab and host all cluster-local certificates using SNI and return those certificates to the caller.

Prerequisites

The following tasks have to be done upfront:

• [cluster-local-domain-tls] extend our Knative internal CA to sign cluster-local certificates #14216
• [cluster-local-domain-tls] create KnativeCertificate in Serving when cluster-local encryption is enabled #14217

Work

• net-contour needs to read the internal KnativeCertificates and host those using SNI on the cluster-local listener.