fix: Add cups package for PDF font rendering

cups - Common UNIX Printing System(tm)
PPD/driver support, web interface

CUPS is a modular printing system which allows a computer to act as a
print server. A computer running CUPS is a host that can accept print
jobs from client computers, process them, and send them to the
appropriate printer.

build/bench/Dockerfile

@@ -18,6 +18,7 @@ RUN apt-get update -y && apt-get install  \
     fonts-cantarell \
     xfonts-75dpi \
     xfonts-base \
+    cups \
     # to work inside the container
     locales \
     build-essential \