feat: Define src and target repos using vars

This will enable us to define the upstream and downstream repos hosted
external to gitlab (For eg. Github)

.gitlab-ci.yml

@@ -44,9 +44,9 @@ workflow:
   - *get_build_date
   - |
     if [ ! -d $CI_PROJECT_DIR/CRI_XCBC ]; then
-      git clone https://github.com/uabrc/CRI_XCBC.git
       cd CRI_XCBC
-      git remote add upstream https://github.com/jprorama/CRI_XCBC.git
+      git clone ${EXT_PR_TARGET_REPO} ${EXT_REPO_DIR}
+      git remote add upstream ${EXT_PR_SRC_REPO}
       cd ..
     fi
   - cd CRI_XCBC