Add a minimal containerized environment

This patch adds a minimal Zeek environment packaged as a container.
Since this is intended both as a base layer for other images and as a
quick way to explore Zeek we install only zeek and zkg as basic
functionality.

Closes #1625.

docker/Dockerfile

@@ -0,0 +1,60 @@
+# See the file "COPYING" in the main distribution directory for copyright.
+
+# Layer to build Zeek.
+FROM debian:buster-slim AS build_zeek
+
+# Configure system for build.
+RUN apt-get -q update \
+ && apt-get install -q -y --no-install-recommends \
+     bind9 \
+     bison \
+     cmake \
+     flex \
+     g++ \
+     gcc \
+     libmaxminddb-dev \
+     libpcap-dev \
+     libssl-dev \
+     libz-dev \
+     make \
+     python3-minimal \
+     python3-dev \
+     swig \
+     ninja-build \
+     python3-pip \
+ && apt-get clean \
+ && rm -rf /var/lib/apt/lists/*
+
+# Copy over the Zeek source tree.
+# NOTE: This assumes that we build in the context of the parent directory (the
+# Git checkout root). We e.g., ensure that in the `Makefile` in this directory.
+COPY . /src/zeek
+RUN make -C /src/zeek distclean
+
+WORKDIR /src/zeek
+RUN ./configure \
+     --generator=Ninja \
+     --build-type=Release \
+ && ninja -C build install
+
+# Final layer containing all artifacts.
+FROM debian:buster-slim AS final
+
+RUN apt-get -q update \
+ && apt-get install -q -y --no-install-recommends \
+     ca-certificates \
+     git \
+     libmaxminddb0 \
+     libpython3.7 \
+     libpcap0.8 \
+     libssl1.1 \
+     libz1 \
+     python3-minimal \
+     python3-git \
+     python3-semantic-version \
+ && apt-get clean \
+ && rm -rf /var/lib/apt/lists/*
+
+# Copy over Zeek installation.
+COPY --from=build_zeek /usr/local/zeek /usr/local/zeek
+ENV PATH "/usr/local/zeek/bin:${PATH}"