Facilitate testing PRs from an external repo hosted on GH

Closes #129 (closed)

This will enable us to define the upstream and downstream repos along with their respective branches that need to be set as an external repo (i.e. hosted external to gitlab for eg. Github) for this project to function.

.gitlab-ci.yml

@@ -52,15 +52,15 @@ workflow:
   - cd CRI_XCBC
   - git config user.name "${GIT_AUTHOR_NAME}"
   - git config user.email "${GIT_AUTHOR_EMAIL}"
-  - git fetch origin uab-prod
-  - git fetch upstream dev
-  - git checkout uab-prod
-  - git merge origin/uab-prod
+  - git checkout ${EXT_PR_TARGET_BRANCH}
+  - git fetch origin ${EXT_PR_TARGET_BRANCH}
+  - git merge origin/${EXT_PR_TARGET_BRANCH}
   - git checkout -b integration
-  - git merge upstream/dev
   - export CRI_XCBC_HEAD=$(git rev-parse --short HEAD)
   - export CRI_XCBC_dev=$(git rev-parse --short upstream/dev)
   - export CRI_XCBC_prod=$(git rev-parse --short origin/uab-prod)
+  - git fetch upstream ${EXT_PR_SRC_BRANCH}
+  - git merge upstream/${EXT_PR_SRC_BRANCH}
   - cd ..
   - export PACKER_IMAGE_HEAD=$(git rev-parse --short HEAD)
   - echo CRI_XCBC_HEAD=${CRI_XCBC_HEAD} | tee -a $CI_PROJECT_DIR/image.env