Alerting: Next gen Alerting page (#28397)

* create page and sidebar entry

* add components for query editor and definition

* split pane things

* add reducer and action

* implement split pane and update ui actions

* making things pretty

* Unify toolbar

* minor tweak to title prefix and some padding

* can create definitions

* fix default state

* add notificaion channel

* add wrappers to get correct spacing between panes

* include or exclude description

* implement query editor

* start on query result component

* update from master

* some cleanup and remove expressions touch ups

Co-authored-by: Torkel Ödegaard <torkel@grafana.com>

pkg/api/index.go

@@ -196,6 +196,16 @@ func (hs *HTTPServer) getNavTree(c *models.ReqContext, hasEditPerm bool) ([]*dto
 		})
 	}
 
+	if hs.Cfg.IsNgAlertEnabled() {
+		navTree = append(navTree, &dtos.NavLink{
+			Text:     "NgAlerting",
+			Id:       "ngalerting",
+			SubTitle: "Next generation alerting",
+			Icon:     "bell",
+			Url:      setting.AppSubUrl + "/ngalerting",
+		})
+	}
+
 	if c.IsSignedIn {
 		navTree = append(navTree, getProfileNode(c))
 	}