Alerting: Time intervals API (read only endpoints) (#81672)

* declare new API and models GettableTimeIntervals, PostableTimeIntervals
* add new actions alert.notifications.time-intervals:read and alert.notifications.time-intervals:write.
* update existing alerting roles with the read action. Add to all alerting roles.
* add integration tests

pkg/services/ngalert/api/notifications.go

@@ -0,0 +1,34 @@
+package api
+
+import (
+	"net/http"
+
+	"github.com/grafana/grafana/pkg/api/response"
+	contextmodel "github.com/grafana/grafana/pkg/services/contexthandler/model"
+)
+
+type NotificationsApiHandler struct {
+	muteTimingService MuteTimingService
+}
+
+func NewNotificationsApi(muteTimingService MuteTimingService) NotificationsApi {
+	return &NotificationsApiHandler{
+		muteTimingService: muteTimingService,
+	}
+}
+
+func (f *NotificationsApiHandler) handleRouteNotificationsGetTimeInterval(ctx *contextmodel.ReqContext, name string) response.Response {
+	model, err := f.muteTimingService.GetMuteTiming(ctx.Req.Context(), name, ctx.OrgID)
+	if err != nil {
+		return errorToResponse(err)
+	}
+	return response.JSON(http.StatusOK, model) // TODO convert to timing interval
+}
+
+func (f *NotificationsApiHandler) handleRouteNotificationsGetTimeIntervals(ctx *contextmodel.ReqContext) response.Response {
+	model, err := f.muteTimingService.GetMuteTimings(ctx.Req.Context(), ctx.OrgID)
+	if err != nil {
+		return errorToResponse(err)
+	}
+	return response.JSON(http.StatusOK, model) // TODO convert to timing interval
+}