Add wrk2 Docker image for benchmarks.

`wrk2` is a fork of `wrk` with finer-grained calibration and more statistics.

It is not currently used in benchmarks.

PiperOrigin-RevId: 528618354

images/benchmarks/wrk2/Dockerfile.x86_64

@@ -0,0 +1,11 @@
+FROM ubuntu:20.04 as build
+RUN apt-get update && apt-get install -y git build-essential libssl-dev libz-dev
+RUN git clone https://github.com/giltene/wrk2.git /tmp/wrk2 && cd /tmp/wrk2 && make
+
+FROM ubuntu:20.04
+RUN set -x \
+        && apt-get update \
+        && apt-get install -y \
+           wget \
+        && rm -rf /var/lib/apt/lists/*
+COPY --from=build /tmp/wrk2/wrk /bin/wrk2