Add hey sample function

Use it to do load testing and observe scaling.

Signed-off-by: Kyle Brennan <kylos101@gmail.com>

sample-functions/hey/Dockerfile

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+FROM openfaas/classic-watchdog:0.18.1 as watchdog
+
+FROM alpine:3.11
+
+RUN mkdir -p /home/app
+
+COPY --from=watchdog /fwatchdog /usr/bin/fwatchdog
+RUN chmod +x /usr/bin/fwatchdog
+
+# Add non root user
+RUN addgroup -S app && adduser app -S -G app && chown app /home/app
+
+WORKDIR /home/app
+
+# setup hey
+RUN apk --no-cache add curl && curl -o /home/app/hey https://storage.googleapis.com/hey-release/hey_linux_amd64 && chmod +x /home/app/hey
+
+# Change from root user
+USER app
+
+# Setup some timeouts for this function...
+ENV write_timeout="60"
+
+# Run the function
+ENV fprocess="xargs ./hey"
+# Set to true to see request in function logs
+ENV write_debug="false"
+
+EXPOSE 8080
+
+HEALTHCHECK --interval=3s CMD [ -e /tmp/.lock ] || exit 1
+
+CMD ["fwatchdog"]

sample-functions/hey/readme.md

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+# Overview
+
+[`hey` is a HTTP load generator.](https://github.com/rakyll/hey).
+
+This is a OpenFaaS Dockerfile function, it wraps `hey`.
+
+Use it to test your functions!
+
+For example, generate load and watch them scale up and down!!!
+
+## Demo
+
+1. Deploy the `nodeinfo` function
+2. Deploy this function
+3. Send a request like through the `hey` function to load test the `nodeinfo` function
+
+```$
+-m POST -d '{}' http://127.0.0.1:8080/function/nodeinfo.openfaas-fn
+```
+
+## Tips
+
+* `hey` does not randomize the request payload, there's nothing saying you cannot call it a bunch with different payloads, though.
+* `hey` defaults Content-Type to "text/html".
+* `hey` requires parameters to be in a certain order. For example, if you don't use the order above, the post body may be empty.