Simplify Waku Mailserver interface with req/resp

[oskarth]

Problem

Right now the Waku mailserver API is needlessly complex https://specs.vac.dev/specs/waku/mailserver.html and lack of more direct req/resp API makes working with them convoluted and error prone.

Solution

Investigate and propose what a KISS alternative would be with a more simple req/resp, as well what implications it would have for security etc.

Acceptance criteria

RFC / raw spec and PoC (e.g.).

[oskarth]

IIRC you were looking into this before @decanus but not sure it was captured in an issue? Assigning you to capture this, if this isn't reasonable with commitment/time scale please adjust

Also cc @cammellos fyi if you know more about previous efforts here

[oskarth]

See status-im/specs#54 (comment) for historical convo

[decanus]

Started research: vacp2p/rfc#116

[oskarth]

@decanus can we finish this up to a point where we can hand it over to Stimbus with issues for improvements?

Then we can reformulate this in the context of Waku v2 track 1