Notifications for multiple Stash instances

This was originally brought up in BAM-14353 and was closed as being a duplicate of BAM-11409. With the resolution and release of BAM-11409, the issue from BAM-14353 is still present.

The new integrated Stash repository type does not handle notifications to multiple Stash instances (or any instance besides the default instance). No new notification type seems to have been introduced, and adding the existing Stash notification type still does not notify the desired Stash instance.

This breaks gating of pull requests based on successful builds on secondary Stash instances along with any other Stash functionality dependent on the build notification from Bamboo.

Original description:

While application links can be established between Bamboo and multiple Stash instances, notifications are only sent to a single default instance.

If multiple instances are linked, either all instances should be notified by Stash notifications, or a way to specify which instance should be notified should be available when configuring the notification.