DOC: config: reorganize actions into their own section

DOC: config: reorganize actions into their own section

The split of the rulesets from their respective actions has long been
overdue so it's time to do it because it has become extremely difficult
to add simple actions in the documentation, as well as it's hard to find
them.

This commit creates two new sections "4.3 Actions keywords matrix" and
"4.4 Alphabetically sorted actions reference" that enumerates all known
actions, with a check indicating for which rule sets they're valid. This
removes all the repetition, occurrences of "see http-request blah for
details" and significantly reduces the number of keywords listed in the
proxies section. This removes 2245 lines from the proxies section in
exchange of 1608 in these new sections.