remote_allow_ranges: allow inside CIDR specific remote_allow_lists (#540)

This allows you to configure remote allow lists specific to different
subnets of the inside CIDR. Example:

    remote_allow_ranges:
      10.42.42.0/24:
        192.168.0.0/16: true

This would only allow hosts with a VPN IP in the 10.42.42.0/24 range to
have private IPs (and thus don't connect over public IPs).

The PR also refactors AllowList into RemoteAllowList and LocalAllowList to make it clearer which methods are allowed on which allow list.

examples/config.yml

@@ -56,6 +56,14 @@ lighthouse:
     #"10.0.0.0/8": false
     #"10.42.42.0/24": true
 
+  # EXPERIMENTAL: This option my change or disappear in the future.
+  # Optionally allows the definition of remote_allow_list blocks
+  # specific to an inside VPN IP CIDR.
+  #remote_allow_ranges:
+    # This rule would only allow only private IPs for this VPN range
+    #"10.42.42.0/24":
+      #"192.168.0.0/16": true
+
   # local_allow_list allows you to filter which local IP addresses we advertise
   # to the lighthouses. This uses the same logic as `remote_allow_list`, but
   # additionally, you can specify an `interfaces` map of regular expressions