feat: add docker build steps (#4)

Introduce CD pipeline, running after CI workflow runs successfully on main branch.
Builds and pushes Docker image to registry.

Reviewed-on: #4
Co-authored-by: Timo Behrendt <t.behrendt@t00n.de>
Co-committed-by: Timo Behrendt <t.behrendt@t00n.de>

.gitea/workflows/cd.yaml

@@ -0,0 +1,52 @@
+name: CD
+
+on:
+  workflow_run:
+    workflows: 
+      - CI
+    branches:
+      - main
+    types:
+      - completed
+
+env:
+  DOCKER_REGISTRY: gitea.t000-n.de
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+      
+      - name: Set up QEMU
+        uses: docker/setup-qemu-action@v2
+      
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v2
+      
+      - name: Login to Registry
+        uses: docker/login-action@v2
+        with:
+          registry: ${{ env.DOCKER_REGISTRY }}
+          username: ${{ secrets.REGISTRY_USER }}
+          password: ${{ secrets.REGISTRY_PASSWORD }}
+      
+      - name: Get Metadata
+        id: meta
+        run: |
+          echo REPO_NAME=$(echo ${GITHUB_REPOSITORY} | awk -F"/" '{print $2}' | tr '[:upper:]' '[:lower:]') >> $GITHUB_OUTPUT
+          echo REPO_VERSION=$(git describe --tags --always | sed 's/^v//') >> $GITHUB_OUTPUT
+      
+      - name: Build and push
+        uses: docker/build-push-action@v4
+        with:
+          context: .
+          file: ./Dockerfile
+          platforms: |
+            linux/amd64
+            linux/arm64
+          push: true
+          tags: |
+            ${{ env.DOCKER_REGISTRY }}/t.behrendt/${{ steps.meta.outputs.REPO_NAME }}:${{ steps.meta.outputs.REPO_VERSION }}
+            ${{ env.DOCKER_REGISTRY }}/t.behrendt/${{ steps.meta.outputs.REPO_NAME }}:latest