Allow extending batch action items

[derpdead]

Currently the only option for extending processingNotifications is to add external endpoint source for key: @Notifications/store/notification/action/getProcessingNotifications/__before which is not exactly what we would like to do.

• We would like to also extend the extended endpoint profile/batch-action for different statuses and names.
• Need to add $this.$getExtendSlot('@BatchActions/extends/notification/components/Notifications') key for given extending key