MM-7188: Cleaning push notification on every read, not only on channel switch (#9348)

* MM-7188: Cleaning push notification on every read, not only on channel switch

* Removed unnecesary goroutine

* Fixing tests

* Applying suggestion from PR

app/plugin_api.go

@@ -251,7 +251,7 @@ func (api *PluginAPI) AddChannelMember(channelId, userId string) (*model.Channel
 		return nil, err
 	}
 
-	return api.app.AddChannelMember(userId, channel, userRequestorId, postRootId)
+	return api.app.AddChannelMember(userId, channel, userRequestorId, postRootId, false)
 }
 
 func (api *PluginAPI) GetChannelMember(channelId, userId string) (*model.ChannelMember, *model.AppError) {