Add initial action

action.yml

@@ -0,0 +1,20 @@
+name: 'Initialize CI Environment and Repository'
+description: 'Initialize a CI environment with nix (and also checkout the repository recursively with LFS)'
+runs:
+  using: "composite"
+  steps:
+    - name: Setup NIX CI Environment
+      run: |
+        echo "substituters = https://nixpkgs-cache.qo.is?priority=39" >> /etc/nix/nix.conf
+        echo "trusted-public-keys = cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY=" >> /etc/nix/nix.conf
+        nix profile install nixpkgs#git-lfs nixpkgs#gnused
+        mkdir -p ~/.config/nix && cp /etc/nix/nix.conf ~/.config/nix/
+
+    - name: Checkout Repository
+      shell: "nix shell nixpkgs#git-lfs nixpkgs#gnused --command {0}"
+      run: |
+        git lfs install
+        git config --global credential.helper store
+        AUTH_URL=`echo -n "$GITHUB_SERVER_URL" | sed "s%https://%https://oauth2:$GITHUB_TOKEN@%"`
+        # Disable clone protection to pull LFS as well
+        GIT_CLONE_PROTECTION_ACTIVE=false git clone --branch $GITHUB_REF_NAME --recurse-submodules $AUTH_URL/$GITHUB_REPOSITORY .