ci: reduce size of Rust interop-test image

This is an automatic backport of pull request #3926 done by [Mergify](https://mergify.com).

Pull-Request: #3945.

interop-tests/Dockerfile

@@ -1,15 +1,24 @@
 # syntax=docker/dockerfile:1.5-labs
-FROM rust:1.67.0
+FROM rust:1.67.0 as builder
+
+# Install zlib as long as libp2p-websocket requires it: https://github.com/paritytech/soketto/issues/72
+RUN apt-get update && \
+    apt-get download zlib1g && \
+    mkdir /dpkg && \
+    for deb in *.deb; do dpkg --extract $deb /dpkg || exit 10; done
 
 # Run with access to the target cache to speed up builds
 WORKDIR /workspace
 ADD . .
 RUN --mount=type=cache,target=./target \
     --mount=type=cache,target=/usr/local/cargo/registry \
-    cargo build --package interop-tests
+    cargo build --release --package interop-tests
 
 RUN --mount=type=cache,target=./target \
-    mv ./target/debug/ping /usr/local/bin/testplan
+    mv ./target/release/ping /usr/local/bin/testplan
 
+FROM gcr.io/distroless/cc
+COPY --from=builder /usr/local/bin/testplan /usr/local/bin/testplan
+COPY --from=builder /dpkg /
 ENV RUST_BACKTRACE=1
 ENTRYPOINT ["testplan"]