Add support for Customized Scheduled Triggers

Currently, Bamboo jobs kicked off via a Scheduled Trigger do not have any support for overriding variables. It would be useful to allow overriding of these variables (just like "Run customized" allows) per trigger.

In my use case, I want to be able to trigger a plan multiple times a day, but with different variables/customizations on each run. Being able to save this configuration with the plan itself (as triggers) would greatly reduce the complexity of managing this plan otherwise.