wgpeerselector: add wgkex support

[lemoer]

As discussed in the gluon meetup today, we want to allow using wgpeerselector in combination with wgkex.

The only (big) missing piece is an HTTPS request to the broker as done here.

I would suggest to add the request here (after the NTP check):

packages/net/wgpeerselector/files/usr/bin/wgpeerselector

Lines 359 to 375 in 308166e

	if not time_synchronized then
	-- WireGuard requires time to be monotonic (always increasing). If
	-- there was a handshake with a peer once, where we had a higher time
	-- than our current time, this peer will not accept our handshakes
	-- until our current time rises above the we had time when the peer had
	-- the last handshake with us. This usually happens on devices without
	-- real time clock, like embedded routers. When we rebooted and therefore
	-- reset our time, the time is lower and handshakes with our last peer
	-- will fail. Therefore we try to synchronize time by calling ntp.
	--
	-- Another possibility, if a boot counter is implemented is outlined here:
	-- https://lists.zx2c4.com/pipermail/wireguard/2019-February/003850.html
	time_synchronized = self:sync_ntp()
	end
	if #self.queued_peers < 1 then
	self:queue_all_peers()

However, the wgkex broker currently expects requests that include {"domain": "'"$SEGMENT"'", "public_key": "'"$PUBLICKEY"'"} in the http body. From the context of the wgpeerselector this information is not tangible. As of now, the wgpeerselector does not know about "domains", as it does not contain gluon code. So this problem needs to be addressed in some way.

@goligo wants to take a look at this. I am open to discuss this here.