Make grpc server host configurable

[Taucher2003]

Currently, the GRPC host is hardcoded and also doesn't support certificate authentication. While certificate authentication isn't a big problem because we have our own authentication, the host should be configurable.

sagittarius/lib/sagittarius/grpc/launcher.rb

Lines 18 to 19 in 2715ec4

	# TODO: make this configurable
	@server.add_http2_port(HOST, :this_port_is_insecure)

This should instead be taken from our configuration system in Sagittarius::Configuration