Add dockerfile and ci config

.gitea/workflows/build.yaml

@@ -0,0 +1,41 @@
+name: Build Flutter SDK Docker Image
+on:
+  schedule:
+    - cron: '0 4 * * 0'
+  workflow_run:
+    types:
+      - requested
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+
+### Setup
+
+      - name: Install docker
+        uses: papodaca/install-docker-action@main
+
+      - name: Install dependencies
+        run: apt update && apt install -y curl
+
+      - name: Check out repository code
+        uses: actions/checkout@v3
+      
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v3
+
+      - name: Login to Docker Registry
+        uses: docker/login-action@v3
+        with:
+          registry: ${{ vars.DOCKER_REGISTRY_HOST }}
+          username: ${{ secrets.DOCKER_REGISTRY_USERNAME }}
+          password: ${{ secrets.DOCKER_REGISTRY_PASSWORD }}
+
+### Build and push docker image
+
+      - name: Build and push, channel 'stable'
+        run: |
+          export CHANNEL=stable
+          export IMAGE_WITH_TAG=${{ vars.DOCKER_REGISTRY_HOST }}/${{ vars.DOCKER_REPO_AND_IMAGE }}:stable
+          docker buildx build . --build-arg CHANNEL=$CHANNEL -t $IMAGE_WITH_TAG --no-cache --push