build: Install fonts from xml2rfc-fonts

Fixes ietf-tools#6294

docker/app.Dockerfile

@@ -55,6 +55,14 @@ RUN groupmod --gid $USER_GID $USERNAME \
 # Switch to local dev user
 USER dev:dev
 
+# Install required fonts
+RUN mkdir -p ~/.fonts/opentype /tmp/fonts && \
+    wget -q -O /tmp/fonts.tar.gz https://github.com/ietf-tools/xml2rfc-fonts/archive/refs/tags/3.18.0.tar.gz && \
+    tar zxf /tmp/fonts.tar.gz -C /tmp/fonts && \
+    mv /tmp/fonts/*/noto/* ~/.fonts/opentype/ && \
+    mv /tmp/fonts/*/roboto_mono/* ~/.fonts/opentype/ && \
+    rm -rf /tmp/fonts.tar.gz /tmp/fonts/
+
 # Install current datatracker python dependencies
 COPY requirements.txt /tmp/pip-tmp/
 RUN pip3 --disable-pip-version-check --no-cache-dir install --user --no-warn-script-location -r /tmp/pip-tmp/requirements.txt