Use GitHub Actions to check for Dockerfile correctness (#14783)

* Use GitHub Actions to check for Dockerfile correctness

* Wait for the health check API endpoint

.github/workflows/docker.yml

+name: Docker
+
+on:
+  pull_request:
+    paths:
+    - 'Dockerfile'
+    - '.github/workflows/docker.yml'
+
+jobs:
+
+  build:
+    runs-on: ubuntu-20.04
+    timeout-minutes: 40
+    steps:
+    - uses: actions/checkout@v2
+    - name: Build container image
+      run: docker build -t test-container-image .
+    - name: Launch container
+      run: docker run -dp 3000:3000 test-container-image
+      timeout-minutes: 5
+    - run: docker ps
+    - name: Wait for Metabase to start
+      run: while ! curl -s localhost:3000/api/health; do sleep 1; done
+      timeout-minutes: 1
+    - name: Check API health
+      run: curl -s localhost:3000/api/health
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