DOC: config: Update documentation about local haproxy response

DOC: config: Update documentation about local haproxy response

Documentation about 'L' state in the termination state was outdated. Today,
not only the request may be intercepted, but also the response.
Documentation about 'L' must be more generic.

However, documentation about possible 2-letter termination states was also
extended to add 'LC' and 'LH' in the list. And 'LR' was adapted too.

This patch should fix the issue #2384. It may be backported to every stable
versions. Note that on 2.8 and lowers, we talk about session and not stream.