Alerting: Protected fields for Contact points (#115442)

* Alerting: Protect sensitive fields of contact points from
 unauthorized modification

- Introduce a new permission alert.notifications.receivers.protected:write. The permission is granted to contact point administrators.
- Introduce field Protected to NotifierOption
- Introduce DiffReport for models.Integrations with focus on Settings. The diff report is extended with methods that return all keys that are different between two settings.
- Add new annotation 'grafana.com/access/CanModifyProtected' to Receiver model
- Update receiver service to enforce the permission and return status 403 if unauthorized user modifies protected field
- Update receiver testing API to enforce permission and return status 403 if unauthorized user modifies protected field.
- Update UI to disable protected fields if user cannot modify them

pkg/services/ngalert/models/testing.go

@@ -1457,6 +1457,12 @@ func (n IntegrationMutators) AddSecureSetting(key, val string) Mutator[Integrati
 	}
 }
 
+func (n IntegrationMutators) RemoveSetting(key string) Mutator[Integration] {
+	return func(c *Integration) {
+		delete(c.Settings, key)
+	}
+}
+
 func randomMapKey[K comparable, V any](m map[K]V) (K, V) {
 	randIdx := rand.Intn(len(m))
 	i := 0