add exec runner

runner-exec/Dockerfile

@@ -0,0 +1,9 @@
+FROM alpine:latest
+
+RUN echo 'http://dl-cdn.alpinelinux.org/alpine/edge/community' >> /etc/apk/repositories
+RUN apk update --no-cache
+RUN apk add --no-cache git curl jq yq python3 docker-cli
+RUN ln -s /usr/bin/python3 /usr/bin/python
+
+COPY ./drone-runner-exec /bin/
+CMD ["drone-runner-exec"]