add target platform for dockerfile, mutli arch image builds

Dockerfile

@@ -5,14 +5,23 @@ FROM node:18@sha256:d0bbfdbad0bff8253e6159dcbee42141db4fc309365d5b8bcfce46ed7156
 WORKDIR /headlamp-plugins
 
 # Add a build argument for the desired plugin to be built
+# Add multi-arch build arguments
 ARG PLUGIN
+ARG TARGETPLATFORM
+ARG TARGETARCH
 
 # Check if the PLUGIN argument is provided
 RUN if [ -z "$PLUGIN" ]; then \
       echo "Error: PLUGIN argument is required"; \
       exit 1; \
     fi
 
+# Enforce that TARGETARCH is specified
+RUN if [ -z "$TARGETARCH" ]; then \
+      echo "Error: TARGETARCH argument is required"; \
+      exit 1; \
+    fi
+
 # Create a directory for the plugin build
 RUN mkdir -p /headlamp-plugins/build/${PLUGIN}
 
@@ -41,6 +50,7 @@ COPY --from=builder /headlamp-plugins/build/ /plugins/
 
 LABEL org.opencontainers.image.source=https://github.com/headlamp-k8s/plugins
 LABEL org.opencontainers.image.licenses=MIT
+LABEL org.opencontainers.image.platform=$TARGETPLATFORM
 
 # Set the default command to list the installed plugins
 CMD ["sh", "-c", "echo Plugins installed at /plugins/:; ls /plugins/"]