Add metric warning support (announcement bar and DM) (#14483)

* Admin. Advisory: Add warning for number of active users metric status

Co-authored-by: Catalin Tomai <catalin.tomai@mattermost.com>

app/app_iface.go

@@ -692,6 +692,7 @@ type AppIface interface {
 	GetUsersWithoutTeamPage(options *model.UserGetOptions, asAdmin bool) ([]*model.User, *model.AppError)
 	GetVerifyEmailToken(token string) (*model.Token, *model.AppError)
 	GetViewUsersRestrictions(userId string) (*model.ViewUsersRestrictions, *model.AppError)
+	GetWarnMetricsStatus() (map[string]*model.WarnMetricStatus, *model.AppError)
 	HTTPService() httpservice.HTTPService
 	Handle404(w http.ResponseWriter, r *http.Request)
 	HandleCommandResponse(command *model.Command, args *model.CommandArgs, response *model.CommandResponse, builtIn bool) (*model.CommandResponse, *model.AppError)
@@ -753,6 +754,7 @@ type AppIface interface {
 	NewPluginAPI(manifest *model.Manifest) plugin.API
 	Notification() einterfaces.NotificationInterface
 	NotificationsLog() *mlog.Logger
+	NotifyAndSetWarnMetricAck(warnMetricId string, sender *model.User, forceAck bool, isBot bool) *model.AppError
 	OpenInteractiveDialog(request model.OpenDialogRequest) *model.AppError
 	OriginChecker() func(*http.Request) bool
 	PatchChannel(channel *model.Channel, patch *model.ChannelPatch, userId string) (*model.Channel, *model.AppError)