MINOR: haterm: add haterm HTTP server

MINOR: haterm: add haterm HTTP server

Contrary to haproxy, httpterm does not support all the HTTP protocols.
Furthermore, it has become easier to handle inbound/outbound
connections / streams since the rework done at conn_stream level.

This patch implements httpterm HTTP server services into haproxy. To do
so, it proceeds the same way as for the TCP checks which use only one
stream connector, but on frontend side.

The makefile is modified to handle haterm.c in additions to all the C
files for haproxy to build new haterm program into haproxy, the haterm
server also instantiates a haterm stream (hstream struct) attached to a
stream connector for each incoming connection without backend stream
connector. This is the role of sc_new_from_endp() called by the muxes to
instantiate streams/hstreams.

As for stream_new(), hstream_new() instantiates a task named
process_hstream() (see haterm.c) which has the same role as
process_stream() but for haterm streams.

haterm into haproxy takes advantage of the HTTP muxes and HTX API to
support all the HTTP protocols supported by haproxy.