ci: refactor CI stages

Signed-off-by: Klagarge <remi@heredero.ch>

web-app/.gitlab-ci.yml

@@ -5,11 +5,11 @@ default:
   image: $DOCKER_IMAGE
 
 stages:
-  - build-docker
+  - web-app-build
 
-docker-build:
+web-app-docker-build:
   image: docker:latest
-  stage: build-docker
+  stage: web-app-build
   services:
     - docker:dind
   script: