Eventing TLS: support path-based routing for MessageReceiver

[pierDipi]

As the Eventing TLS feature track describes we should support TLS for InMemoryChannel.

In particular, the IMC controller will expose an HTTPS address (as part of #6864) that is pointing to the IMC dispatcher.

The https endpoint should be handled differently than the current http endpoint, the reason is described here:
https://docs.google.com/document/d/1H-x_oji8LqkCyd7tlsSyclmUe7FAmEJPgRxOU_0pkn8/edit?resourcekey=0-lzDIPJsZOP3G17QE_g1lHw#heading=h.eg1aqbb7nwxg and it is reported below:

InMemoryChannel
The imc-dispatcher deployment will read (and watch for rotation) a secret containing the TLS public/private key pair in a well-known Secret imc-dispatcher-tls in the system namespace to instantiate the TLS server.

To avoid using wildcard certificates and complex SNI negotiation, we enable IMC dispatcher to use path-based routing for HTTPS requests instead of using host-based routing based on the external name service, and in that case, certificate DNS name must be: imc-dispatcher.knative-eventing.svc..

Given that the DNS name for the certificate will be imc-dispatcher.knative-eventing.svc.<cluster-domain> and we need to distinguish between different channels, so the https address for a given InMemoryChannel will be: https://imc-dispatcher.knative-eventing.svc.<cluster-domain>/<channel-namespace>/<channel-name>, therefore host-based routing that is currently supported by the MessageReceiver (see https://github.com/knative/eventing/blob/main/pkg/channel/message_receiver.go) component should be enhanced to also support serving channels with a path based routing approach.

This issue is scoped to the MessageReceiver library, a followup issue will be created and linked to make use of this enhancement in the IMC dispatcher.

Additional Info

• https://docs.google.com/document/d/1H-x_oji8LqkCyd7tlsSyclmUe7FAmEJPgRxOU_0pkn8/edit?resourcekey=0-lzDIPJsZOP3G17QE_g1lHw#
• https://github.com/knative/eventing/blob/main/pkg/channel/message_receiver.go
• We should try to make use of the server side library created as part of Eventing TLS: support K_CA_CERTS in adapter/v2 #6848

[gab-satchi]

/assign