feat: read Dockerfile from local file system

.vscode/settings.json

@@ -0,0 +1,3 @@
+{
+  "cSpell.words": ["elif", "kaniko"]
+}

action.yml

@@ -1,17 +1,17 @@
 ---
-
 name: Kaniko
 description: Build a container image using Kaniko
 inputs:
-  Dockerfile:
+  dockerfile:
     description: The Dockerfile to pass to Kaniko
-    required: true
+    required: false
   image:
     description: Name and tag under which to upload the image
     required: true
   registry:
     description: Domain of the registry. Should be the same as the first path component of the tag.
-    required: true
+    required: false
+    default: https://index.docker.io/v1/
   username:
     description: Username for the container registry
     required: true
@@ -27,7 +27,16 @@ runs:
     - |
       mkdir -p /kaniko/.docker
       echo '{"auths":{"${{ inputs.registry }}":{"auth":"'$(printf "%s:%s" "${{ inputs.username }}" "${{ inputs.password }}" | base64 | tr -d '\n')'"}}}' > /kaniko/.docker/config.json
-      cat > Dockerfile <<EOF
-      ${{ inputs.Dockerfile }}
-      EOF
-      /kaniko/executor --dockerfile Dockerfile --destination ${{ inputs.image }}
+
+      if [ -n "${{ inputs.dockerfile }}" ]; then
+        echo "Using Dockerfile from input"
+        echo "${{ inputs.dockerfile }}" > Dockerfile
+      elif [ -f "./Dockerfile" ]; then
+        echo "Using existing ./Dockerfile from workspace"
+        cp ./Dockerfile Dockerfile
+      else
+        echo "ERROR: No Dockerfile provided and no ./Dockerfile found in workspace"
+        exit 1
+      fi
+
+      /kaniko/executor --dockerfile Dockerfile --destination "${{ inputs.image }}"