cmdline: add listconfig/helpconfig

[ecdsa]

This adds commands to view the list of config variables

[accumulator]

These commands should not require a running daemon, but currently require either a running daemon or an explicit --offline (but I guess this applies to more commands, as e.g. setconfig/getconfig also require --offline currently)

[accumulator]

minor nitpick: helpconfig use_gossip returns Use trampoline routing

[ecdsa]

The --offline syntax requirement is off-topic. This syntax is explicitly needed for all commands, regardless of whether they use the network, because it clarifies whether the command uses the running daemon or not.

[SomberNight]

I am not sure we need the --more option. How about combining the two descriptions?
e.g.:

Suggested change

	async def helpconfig(self, key, more=False):
	"""Returns help about a configuration variable. """
	cv = self.config.cv.from_key(key)
	return cv.get_long_desc() if more else cv.get_short_desc()
	async def helpconfig(self, key):
	"""Returns help about a configuration variable. """
	cv = self.config.cv.from_key(key)
	short = cv.get_short_desc()
	long = cv.get_long_desc()
	if short and long:
	return short + "\n---\n\n" + long
	else:
	return short or long