BUG/MEDIUM: proto_htx: Introduce the state ENDING during forwarding

BUG/MEDIUM: proto_htx: Introduce the state ENDING during forwarding

This state is used in the legacy HTTP when everything was received from an
endpoint but a filter doesn't forward all the data. It is used to not report a
client or a server abort, depending on channels flags.

The same must be done on HTX streams. Otherwise, the message may be
truncated. For instance, it may happen with the filter trace with the random
forwarding enabled on the response channel.

This patch must be backported to 1.9.