transports/noise: Expose Prologue mechanism

[mxinden]

Description

Enable users to provide a Noise Prologue via Builder::prologue.

Motivation

Needed for #2622, more specifically to validate the remote's TLS fingerprints. See libp2p/specs#412 (comment).

Requirements

Open questions

Are you planning to do it yourself in a pull request?

Maybe. In case someone wants to pick this up instead, please comment to make sure we are not duplicating work.

[mxinden]

Corresponding pull request on the Golang side: libp2p/go-libp2p#1663

[thomaseizinger]

@melekes Let me know if you are going to pick this up, otherwise I'll take it :)

[melekes]

Please go ahead. I will focus more on smoldot / substrate side for now.