Alerting: refactor notifiers to use package specific Logger interface (#60361)

* introduce Logger interface local to channles + implementaton that wraps the Grafana logger
* make NewFactoryConfig accept LoggerFactory
* add logger field to FactoryConfig
* update usages of log.Logger to internal interface

pkg/services/sqlstore/migrations/ualert/ualert.go

@@ -500,7 +500,9 @@ func (m *migration) validateAlertmanagerConfig(orgID int64, config *PostableUser
 			if !exists {
 				return fmt.Errorf("notifier %s is not supported", gr.Type)
 			}
-			factoryConfig, err := channels.NewFactoryConfig(cfg, nil, decryptFunc, nil, nil)
+			factoryConfig, err := channels.NewFactoryConfig(cfg, nil, decryptFunc, nil, nil, func(ctx ...interface{}) channels.Logger {
+				return &channels.FakeLogger{}
+			})
 			if err != nil {
 				return err
 			}