cirrus: Use ccache for faster container builds

docker/builder.Dockerfile

@@ -0,0 +1,29 @@
+# See the file "COPYING" in the main distribution directory for copyright.
+
+# Layer to build Zeek.
+FROM debian:bullseye-slim
+
+# Configure system for build.
+RUN apt-get -q update \
+ && apt-get install -q -y --no-install-recommends \
+     bind9 \
+     bison \
+     ccache \
+     cmake \
+     flex \
+     g++ \
+     gcc \
+     libfl2 \
+     libfl-dev \
+     libmaxminddb-dev \
+     libpcap-dev \
+     libssl-dev \
+     libz-dev \
+     make \
+     python3-minimal \
+     python3.9-dev \
+     swig \
+     ninja-build \
+     python3-pip \
+ && apt-get clean \
+ && rm -rf /var/lib/apt/lists/*

docker/final.Dockerfile

@@ -0,0 +1,25 @@
+# See the file "COPYING" in the main distribution directory for copyright.
+
+# Final layer containing all artifacts.
+FROM debian:bullseye-slim
+
+RUN apt-get -q update \
+ && apt-get install -q -y --no-install-recommends \
+     ca-certificates \
+     git \
+     libmaxminddb0 \
+     libpython3.9 \
+     libpcap0.8 \
+     libssl1.1 \
+     libz1 \
+     python3-minimal \
+     python3-git \
+     python3-semantic-version \
+     python3-websocket \
+ && apt-get clean \
+ && rm -rf /var/lib/apt/lists/*
+
+# Copy over Zeek installation from build
+COPY --from=zeek-build /usr/local/zeek /usr/local/zeek
+ENV PATH "/usr/local/zeek/bin:${PATH}"
+ENV PYTHONPATH "/usr/local/zeek/lib/zeek/python:${PYTHONPATH}"