Move away from the documentation-builder image

Its purpose is rather dubious nowadays, we should probably drop it.

.gitlab-ci.yml

@@ -54,10 +54,21 @@ test-html:
     - public
 
 .gen-pdf:
-  image: registry.gitlab.apertis.org/infrastructure/apertis-docker-images/v2022-documentation-builder
+  image: debian:buster-slim
   stage: generate-pdf
   tags:
     - lightweight
+  before_script:
+  - apt update && apt install -y
+      fonts-freefont-ttf
+      fonts-noto
+      librsvg2-bin
+      lmodern
+      pandoc
+      python-lxml
+      python3
+      python3-pandocfilters
+      texlive-xetex
   script:
   - echo "Building PDFs on $(nproc) cores"
   - find public -name "*.pdf-in" -print0 | xargs -0 -r -n1 -P "$(nproc)" scripts/create-pdf