Implement Rollback with Release Management for TFS 2015

Introduces a rollback strategy for Azure DevOps Server deployments using the 'Rollback powershell' task from the Release Management Utility Tasks extension. Details how to use the `Release_Tasks` environment variable to detect failed tasks and execute selective rollback scripts. Provides an example of a deployment workflow with backup, deploy, configure, and rollback steps, emphasizing the 'Always Run' setting for the rollback task.