[CI] Allow each stage of pipeline to be launched manually

The pipeline will automatically build the image whenever some files are changed.

But for some tasks, you may want to enable certain stages manually.
This is what this commit does.

.gitlab-ci.yml

@@ -56,14 +56,18 @@ set-variables:
   script:
     - chmod +x ./get-modified-image.sh
     - ./get-modified-image.sh
+  # If the Dockerfile is changed, force the build.
+  # Otherwise, may be triggered manually.
+  rules:
+    - changes:
+      - **/Dockerfile
+      - **/docker-compose.yml
+      when: always
+    - when: manual
   only:
-    changes:
-      - "**/Dockerfile"
-      - "**/docker-compose.yml"
     refs:
       - master
       - dev-ci
-      - dev-sympa
 
 # Build the image that was modified
 build:
@@ -78,9 +82,14 @@ build:
     - docker push $MODIFIED_IMAGE_FULL_TEST
   after_script:
     - docker logout $REGISTRY
+  # If the Dockerfile is changed, force the build.
+  # Otherwise, may be triggered manually.
+  rules:
+    - changes:
+      - **/Dockerfile
+      when: always
+    - when: manual
   only:
-    changes:
-      - "**/Dockerfile"
     refs:
       - master
       - dev-ci
@@ -101,11 +110,14 @@ clair:
     paths:
       - clair-report.json
       - clair.log
-  only:
-    changes:
+  rules:
+    - changes:
       - "**/Dockerfile"
       - "**/docker-compose.yml"
       - "**/clair-whitelist.yml"
+      when: always
+    - when: manual
+  only:
     refs:
       - master
       - dev-ci
@@ -133,10 +145,13 @@ docker-bench-security:
       - report.txt
   after_script:
     - docker logout $REGISTRY
-  only:
-    changes:
+  rules:
+    - changes:
       - "**/Dockerfile"
       - "**/docker-compose.yml"
+      when: always
+    - when: manual
+  only:
     refs:
       - master
       - dev-ci
@@ -155,9 +170,6 @@ push-prod:
   after_script:
     - docker logout $REGISTRY_PROD
   only:
-    changes:
-      - "**/Dockerfile"
-      - "**/docker-compose.yml"
     refs:
       - master
       - dev-ci