introduce github action to build iso

.github/workflows/main.yaml

@@ -0,0 +1,41 @@
+name: Build iPXE
+
+on:
+  push:
+    tags:
+      - 'v*-hetzner*'
+
+jobs:
+  build_iso:
+    name: Build ISO
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - name: install build dependencies
+        run: |
+          sudo apt-get update
+          sudo apt-get -y install \
+            isolinux \
+            genisoimage
+      - name: build cloud/hetzner
+        run: make -C src bin/ipxe.iso CONFIG=cloud EMBED=config/cloud/hetzner.ipxe
+      - name: Create Release
+        id: create_release
+        uses: actions/create-release@v1
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        with:
+          tag_name: ${{ github.ref }}
+          release_name: Release ${{ github.ref }}
+          draft: false
+          prerelease: false
+      - name: Upload Release Asset
+        id: upload-release-asset 
+        uses: actions/upload-release-asset@v1
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        with:
+          upload_url: ${{ steps.create_release.outputs.upload_url }} # This pulls from the CREATE RELEASE step above, referencing it's ID to get its outputs object, which include a `upload_url`. See this blog post for more info: https://jasonet.co/posts/new-features-of-github-actions/#passing-data-to-future-steps 
+          asset_path: src/bin/ipxe.iso
+          asset_name: ipxe-hetzner.iso
+          asset_content_type: application/x-iso9660-image

src/config/cloud/hetzner.ipxe

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+#!ipxe
+
+echo Hetzner Cloud - iPXE boot via user-data
+echo CPU: ${cpuvendor} ${cpumodel}
+ifstat ||
+dhcp ||
+route ||
+chain -ar http://169.254.169.254/latest/user-data