MINOR: config: add a function to dump all known config keywords

MINOR: config: add a function to dump all known config keywords

All registered config keywords that are valid in the config parser are
dumped to stdout organized like the regular sections (global, listen,
etc). Some keywords that are known to only be valid in frontends or
backends will be suffixed with [FE] or [BE].

All regularly registered "bind" and "server" keywords are also dumped,
one per "bind" or "server" line. Those depending on ssl are listed after
the "ssl" keyword. Doing so required to export the listener and server
keyword lists that were static.

The function is called from dump_registered_keywords() for keyword
class "cfg".