add docker image building step to e2e test workflow

.github/workflows/test-e2e.yml

@@ -2,8 +2,46 @@ name: ocelot.social end-to-end test CI
 on: push
 
 jobs:
+  docker_preparation:
+    name: Fullstack test preparation
+    runs-on: ubuntu-latest
+    outputs:
+      pr-number: ${{ steps.pr.outputs.number }}
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v3
+
+      - name: Copy env files
+        run: |
+          cp webapp/.env.template webapp/.env
+          cp backend/.env.template backend/.env
+
+      - name: Build docker images
+        run: |
+          mkdir /tmp/images
+          docker build --target community -t "ocelotsocialnetwork/neo4j-community:test" neo4j/
+          docker save "ocelotsocialnetwork/neo4j-community:test" > /tmp/images/neo4j.tar
+          docker build --target test -t "ocelotsocialnetwork/backend:test" backend/
+          docker save "ocelotsocialnetwork/backend:test" > /tmp/images/backend.tar
+          docker build --target test -t "ocelotsocialnetwork/webapp:test" webapp/
+          docker save "ocelotsocialnetwork/webapp:test" > /tmp/images/webapp.tar
+
+      - name: Get pr number
+        id: pr
+        uses: 8BitJonny/gh-get-current-pr@2.2.0
+      
+      - name: Cache docker images
+        id: cache
+        uses: actions/cache/save@v3.3.1
+        with:
+          path: |
+            /tmp/images/
+          key: e2e-preparation-cache-pr${{ steps.pr.outputs.number }}
+
   fullstack_tests:
     name: Fullstack tests
+    if: success()
+    needs: docker_preparation
     runs-on: ubuntu-latest
     env:
       jobs: 8