Trying to automate building the flatpak docker image build

.gitlab-ci.yml

@@ -1,4 +1,5 @@
 stages:
+  - build-containers
   - test
   - build
   - deploy
@@ -47,7 +48,7 @@ build:
       - dist/*
 
 build_flatpak:
-    image: registry.gitlab.com/sumner/sublime-music/sublime-music/build:latest
+    image: registry.gitlab.com/sumner/sublime-music/flatpak-build:latest
     stage: build
     script:
       - cd flatpak
@@ -78,3 +79,18 @@ verify_deploy:
     - master
   script:
     - pip3 install libremsonic
+
+# Create the Docker image for Flatpak builds.
+docker:image:
+  image: docker:1.13
+  only:
+    variables:
+      - $REBUILD_FLATPAK_DOCKER == "True"
+  services:
+    - docker:dind
+  script:
+    - docker version
+    - docker build -t $CI_REGISTRY_IMAGE/flatpak-build:latest ./cicd/flatpak-build
+    - docker login -u gitlab-ci-token -p $CI_BUILD_TOKEN $CI_REGISTRY
+    - docker push $CI_REGISTRY_IMAGE/build
+  stage: build-containers