Use prebuild docker image for backend

.gitlab-ci.yml

@@ -1,18 +1,15 @@
-image: ubuntu:latest
-
 stages:
     - build
     - package
 
 build_backend:
     stage: build
+    image: reg.gitlab.mattv.de/root/docker-images/ubuntu_build_base:latest
     cache:
         key: backend
         paths:
             - vcpkg_cache
     script:
-        - apt-get update
-        - apt-get install g++ gcc make cmake git curl zip unzip tar python3 pkg-config -y
         - SRC="$PWD"
         - TMP=$(mktemp -d)
         - cd $TMP
@@ -45,6 +42,7 @@ test_and_build_frontend:
             - frontend/dist/
 
 package_server:
+    image: alpine:latest
     stage: package
     before_script: []
     needs: