Reduce final image size

These optimizations reduce the final image size by over 60%.

Dockerfile

@@ -1,18 +1,31 @@
-FROM debian:latest
+FROM debian:bullseye-slim
 
-# Used in the makefile
-ENV CHORDPRO_PIPELINE true
+ENV CHORDPRO_PIPELINE=true
 
 ARG ZOLA_VERSION="0.21.0"
 ARG CHORDPRO_VERSION="6.090.0"
 
-RUN apt update -y && apt-get install -y --no-install-recommends \
-    ca-certificates openssl openssh-client rsync git wget build-essential cpanminus libio-socket-ssl-perl ghostscript nodejs
-RUN update-ca-certificates
-RUN cpanm chordpro@${CHORDPRO_VERSION}
-RUN wget https://github.com/getzola/zola/releases/download/v${ZOLA_VERSION}/zola-v${ZOLA_VERSION}-x86_64-unknown-linux-gnu.tar.gz && \
-    tar -xvzf zola-v${ZOLA_VERSION}-x86_64-unknown-linux-gnu.tar.gz && \
-    mv zola /usr/local/bin/zola && \
-    rm zola-v${ZOLA_VERSION}-x86_64-unknown-linux-gnu.tar.gz
+# Install runtime dependencies only, clean up after
+RUN apt-get update && apt-get install -y --no-install-recommends \
+    ca-certificates \
+    openssl \
+    openssh-client \
+    rsync \
+    git \
+    wget \
+    libio-socket-ssl-perl \
+    ghostscript \
+    nodejs \
+ && rm -rf /var/lib/apt/lists/*
+
+RUN apt-get update && apt-get install -y --no-install-recommends build-essential cpanminus \
+ && cpanm chordpro@${CHORDPRO_VERSION} \
+ && apt-get purge -y --auto-remove build-essential cpanminus \
+ && rm -rf /root/.cpanm /var/lib/apt/lists/*
+
+RUN wget -q https://github.com/getzola/zola/releases/download/v${ZOLA_VERSION}/zola-v${ZOLA_VERSION}-x86_64-unknown-linux-gnu.tar.gz \
+ && tar -xzf zola-v${ZOLA_VERSION}-x86_64-unknown-linux-gnu.tar.gz \
+ && mv zola /usr/local/bin/ \
+ && rm zola-v${ZOLA_VERSION}-x86_64-unknown-linux-gnu.tar.gz
 
 CMD ["/bin/sh"]