Support "rollback"

[kmanning]

• Support the ability to "rollback" a deployment that you do not like (eg: rollback to a successful deployment, if the most recent deployment failed).
• Options:
  • When the pipeline runs, it automatically pulls from master. Add a new feature where running the pipeline will prompt the user for a git commit. Allow the user to select a git commit for the last successful deployment. If that is chosen, redeploy that commit (effectively, rollback by redeploying the last successful deployment.) If the user does not choose this option, continue with the default behavior, and deploy the lasted commit from master. Make sure this "works" when running in a branch, where 'terraform apply' is not available.

[kmanning]

Closing this - this is basically only possible with a Declarative Pipeline. See issue #42 on possible ideas for getting as close as possible to this.