Add docker-rust image

ci/docker-rust/Dockerfile

@@ -0,0 +1,13 @@
+FROM rust
+
+RUN apt update && \
+    apt-get install apt-transport-https && \
+    echo deb https://apt.buildkite.com/buildkite-agent stable main > /etc/apt/sources.list.d/buildkite-agent.list && \
+    apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv-keys 32A37959C2FA5C3C99EFBC32A79206696452D198 && \
+    apt update && \
+    apt install -y \
+      buildkite-agent \
+      rsync \
+      sudo \
+      && \
+    rm -rf /var/lib/apt/lists/*