Move TARGET_BRANCH var back to template file

Background

The CHT pipeline uses a variable named TARGET_BRANCH to define which branch of the pipeline code should be cloned in our preflight stage. This variable is defined with the dsop group. When testing pipeline-test-projects, the POPs group needs to add a variable at pipeline runtime of TARGET_BRANCH, in order to override the default value and test their feature branch of the pipeline. If POPs members were able to add a variable to their .gitlab-ci.yml file, it would allow for multiple members to test on the same test project more easily, and would prevent having to cancel pipelines created from commits to the test project, as they are currently not able to override the target branch var.

DoD

• Add TARGET_BRANCH to variables section of templates/globals.yaml
• Remove TARGET_BRANCH GitLab CI var in the dsop group

AC

• Validate change by running the following projects
  • UBI based image: Enter Project Name Here
  • Distroless based project: Enter Project Name Here
• Test pipeline-test-project's use of variable: TARGET_BRANCH w/in .gitlab-ci.yml file
  • Enter Project Name Here