install buildx

Signed-off-by: Brooks Newberry <brooks@newberry.com>

Dockerfile.dapper

@@ -17,6 +17,9 @@ RUN if [ "${ARCH:-$(go env GOARCH)}" = "amd64" ]; then \
         curl -sL "https://github.com/docker/compose/releases/download/v2.17.3/docker-compose-linux-x86_64" -o /usr/local/bin/docker-compose && \
         chmod +x /usr/local/bin/docker-compose; \
     fi
+RUN mkdir -p /usr/local/lib/docker/cli-plugins; \
+    curl -o /usr/local/lib/docker/cli-plugins/docker-buildx -fsSL "https://github.com/docker/buildx/releases/download/v0.11.2/buildx-v0.11.2.linux-${ARCH}"; \
+    chmod +x /usr/local/lib/docker/cli-plugins/docker-buildx
 ENV DAPPER_ENV REPO TAG DRONE_TAG
 ENV DAPPER_SOURCE /go/src/github.com/rancher/system-upgrade-controller/
 ENV DAPPER_OUTPUT ./bin ./dist