Introduce two new system properties in Bamboo that allow users to control the default behaviour of the "Delete plan branch" plan configuration properties.

Background

Currently, the "Delete plan branch" plan configuration properties, such as "After branch was deleted from repository" and "After branch inactivity in repository" are disabled by default. Some customers may prefer these properties to be enabled by default or at least controllable.

Feature Requirements:

1. Add two new system properties for controlling the default behaviour of the "Delete plan branch" plan configuration properties
   • -Dbamboo.plan.branch.delete.when.removed.from.vcs
   • -Dbamboo.plan.branch.delete.when.inactive.in.vcs
2. Both properties should default to false to keep the default behaviour
3. Ensure that these properties are only applied to new Plans, leaving current plan configurations unmodified.