build: add Docker based PDF build environment

Addresses #1043

docker/docker-compose.build-pdf.yaml

@@ -0,0 +1,13 @@
+version: '3.8'
+
+services:
+  pdf-builder:
+    build:
+      context: ../
+      dockerfile: docker/images/Dockerfile.pdf-builder
+    image: edb/x-docs-pdf-builder
+    container_name: pdf-builder
+    hostname: pdf-builder
+    working_dir: /app
+    volumes:
+      - ../:/app

docker/images/Dockerfile.pdf-builder

@@ -0,0 +1,27 @@
+FROM ubuntu:focal
+
+ARG PANDOC_VERSION=2.12
+ARG PANDOC_DEB=pandoc-2.12-1-amd64.deb
+ARG WKHTML_TO_PDF_VERSION=0.12.6-1
+ARG WKHTML_TO_PDF_DEB=wkhtmltox_${WKHTML_TO_PDF_VERSION}.focal_amd64.deb
+
+RUN apt-get update && apt-get install --no-install-recommends -y \
+  python3 \
+  wget \
+  && apt-get clean \
+  && rm -rf /var/lib/apt/lists/*
+
+# Install Pandoc
+RUN wget --no-check-certificate -P /tmp https://github.com/jgm/pandoc/releases/download/${PANDOC_VERSION}/${PANDOC_DEB} \
+  && apt-get install --no-install-recommends -y /tmp/${PANDOC_DEB} \
+  && apt-get clean \
+  && rm -rf /var/lib/apt/lists/* \
+  && rm -rf /tmp/*
+
+# Install wkhtmltopdf
+RUN wget --no-check-certificate -P /tmp https://github.com/wkhtmltopdf/packaging/releases/download/${WKHTML_TO_PDF_VERSION}/${WKHTML_TO_PDF_DEB} \
+  && apt-get update \
+  && apt-get install --no-install-recommends -y /tmp/${WKHTML_TO_PDF_DEB} \
+  && apt-get clean \
+  && rm -rf /var/lib/apt/lists/* \
+  && rm -rf /tmp/*