add GitHub Action workflow for DockerfileExtra

Adds build-extra-image.yml workflow with workflow_dispatch trigger
to allow manual builds from the GitHub UI. Supports custom tag input.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

.github/workflows/build-extra-image.yml

@@ -0,0 +1,58 @@
+env:
+  REGISTRY: ghcr.io
+  IMAGE_NAME: ${{ github.repository }}
+
+name: Build windmill-extra
+
+on:
+  workflow_dispatch:
+    inputs:
+      tag:
+        description: "Tag for the image"
+        required: false
+        default: "dev"
+        type: string
+
+permissions: write-all
+
+jobs:
+  build_extra:
+    runs-on: ubicloud
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          ref: ${{ github.ref }}
+          fetch-depth: 0
+
+      - uses: depot/setup-action@v1
+
+      - name: Docker meta
+        id: meta
+        uses: docker/metadata-action@v5
+        with:
+          images: |
+            ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}-extra
+          flavor: |
+            latest=false
+          tags: |
+            type=raw,value=${{ github.event.inputs.tag }}
+            type=sha,enable=true,priority=100,prefix=,suffix=,format=short
+
+      - name: Login to registry
+        uses: docker/login-action@v3
+        with:
+          registry: ${{ env.REGISTRY }}
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Build and push
+        uses: depot/build-push-action@v1
+        with:
+          context: .
+          platforms: linux/amd64,linux/arm64
+          push: true
+          file: "./docker/DockerfileExtra"
+          tags: |
+            ${{ steps.meta.outputs.tags }}
+          labels: |
+            ${{ steps.meta.outputs.labels }}