feat(plugins): Implement event system w/ POC events

Implements the partially created event system with 3 events implemented as proof of concepts.

The 3 events are:
- `blacklistedIpBlocked`: emitted when a request from a blacklisted IP
- `accessRuleCreated`: emitted when a new access rule is created
- `blacklistToggled`: emitted when the blacklist is toggled for a given access rule

Why these events? Because these are the ones I forsee myself needing in the next version of the zoraxy_crowdsec_bouncer

Events are dispatched via a global event manager `plugins.EventSystem.Emit`

src/mod/plugins/lifecycle.go

@@ -151,6 +151,19 @@ func (m *Manager) StartPlugin(pluginID string) error {
 	thisPlugin.process = cmd
 	thisPlugin.Enabled = true
 
+	// Register event subscriptions
+	if thisPlugin.Spec.SubscriptionsEvents != nil {
+		for eventName := range thisPlugin.Spec.SubscriptionsEvents {
+			eventType := zoraxyPlugin.EventName(eventName)
+			err := EventSystem.Subscribe(thisPlugin.Spec.ID, eventType)
+			if err != nil {
+				m.Log("Failed to subscribe plugin "+thisPlugin.Spec.Name+" to event "+eventName, err)
+			} else {
+				m.Log("Subscribed plugin "+thisPlugin.Spec.Name+" to event "+eventName, nil)
+			}
+		}
+	}
+
 	//Create a new static forwarder router for each of the static capture paths
 	thisPlugin.StartAllStaticPathRouters()
 
@@ -288,6 +301,11 @@ func (m *Manager) StopPlugin(pluginID string) error {
 	if err != nil {
 		m.Log("Failed to revoke API keys for plugin "+thisPlugin.Spec.Name, err)
 	}
+	//Unsubscribe from all events
+	err = EventSystem.UnsubscribeAll(thisPlugin.Spec.ID)
+	if err != nil {
+		m.Log("Failed to unsubscribe plugin "+thisPlugin.Spec.Name+" from events", err)
+	}
 
 	return nil
 }