Feature/dns-server (#537)

Adding DNS server for client

Updated the API with new fields

Added custom zone object for peer's DNS resolution

client/internal/dns/mock_test.go

@@ -0,0 +1,25 @@
+package dns
+
+import (
+	"github.com/miekg/dns"
+	"net"
+)
+
+type mockResponseWriter struct {
+	WriteMsgFunc func(m *dns.Msg) error
+}
+
+func (rw *mockResponseWriter) WriteMsg(m *dns.Msg) error {
+	if rw.WriteMsgFunc != nil {
+		return rw.WriteMsgFunc(m)
+	}
+	return nil
+}
+
+func (rw *mockResponseWriter) LocalAddr() net.Addr       { return nil }
+func (rw *mockResponseWriter) RemoteAddr() net.Addr      { return nil }
+func (rw *mockResponseWriter) Write([]byte) (int, error) { return 0, nil }
+func (rw *mockResponseWriter) Close() error              { return nil }
+func (rw *mockResponseWriter) TsigStatus() error         { return nil }
+func (rw *mockResponseWriter) TsigTimersOnly(bool)       {}
+func (rw *mockResponseWriter) Hijack()                   {}