[#17] Add morph client metrics

Signed-off-by: Alejandro Lopez <a.lopez@yadro.com>

pkg/morph/metrics/metrics.go

@@ -0,0 +1,17 @@
+package metrics
+
+import "time"
+
+type Register interface {
+	IncSwitchCount()
+	SetLastBlock(uint32)
+	IncNotificationCount(notificationType string)
+	ObserveInvoke(typ string, contract string, method string, success bool, d time.Duration)
+}
+
+type NoopRegister struct{}
+
+func (NoopRegister) IncSwitchCount()                                           {}
+func (NoopRegister) SetLastBlock(uint32)                                       {}
+func (NoopRegister) IncNotificationCount(string)                               {}
+func (NoopRegister) ObserveInvoke(string, string, string, bool, time.Duration) {}