!htp #16162 Upgrade server- and client-side HTTP APIs to "final style"

This PR clears #16162.
It currently builds on #16383, so ignore Björn's commit in your review.

As a temporary measure I have added a stub TCP API as described by #16166. This `TempTcp` stuff will go away when #16166 is cleared.
Let's take a simple example: We have a simple text based server accepting text commands and replying with text. This is a passive setup. Now I wan't to add a banner that is sent first when the client connects: suddenly it becomes active. In this setting the names passive and active are confusing since the only activeness in the server is just that banner. 

I still don't see why join is more confusing than this dual API. Also, the activeFlow can be embedded in a graph, and in that case adding a banner would be only adding a Concat node with a banner source before emitting the command responses. 

I don't want to hold back this PR though, so if this is the only remaining thing, then merge as it is.