SW-836: Automatically build the correct docker build image

.gitlab-ci.yml

 stages:
+  - prepare
   - build
   - test
 
+#
+# PREPARE STAGE
+#
+
+prepare_RAServices:
+  stage: prepare
+  script:
+    - docker build -t ci_raservices -f SubSystems/RAServices/Dockerfile
+
 #
 # BUILD STAGE
 #