add calculated_remotes

[wadey]

This setting allows us to "guess" what the remote might be for a host while we wait for the lighthouse response. For networks that hard designed with in mind, it can help speed up handshake performance, as well as improve resiliency in the case that all lighthouses are down.

Example:

lighthouse:
  # ...

  calculated_remotes:
    # For any Nebula IPs in 10.0.10.0/24, this will apply the mask and add
    # the calculated IP as an initial remote (while we wait for the response
    # from the lighthouse). Both CIDRs must have the same mask size.
    # For example, Nebula IP 10.0.10.123 will have a calculated remote of
    # 192.168.1.123

    10.0.10.0/24:
      - mask: 192.168.1.0/24
        port: 4242