Allow to convert html->pdf via weasyprint

modules/joex/src/main/resources/reference.conf

@@ -551,6 +551,10 @@ Docpell Update Check
       """
     }
 
+    # Which HTML->PDF converter command to use. One of: wkhtmlpdf,
+    # weasyprint.
+    html-converter = "wkhtmlpdf"
+
     # To convert HTML files into PDF files, the external tool
     # wkhtmltopdf is used.
     wkhtmlpdf {
@@ -568,7 +572,22 @@ Docpell Update Check
         ]
         timeout = "2 minutes"
       }
-      working-dir = ${java.io.tmpdir}"/docspell-convert"
+      working-dir = ${java.io.tmpdir}"/docspell-wkhtmltopdf"
+    }
+
+    # An alternative to wkhtmltopdf is weasyprint.
+    weasyprint {
+      command = {
+        program = "weasyprint"
+        args = [
+          "--optimize-size", "all",
+          "--encoding", "{{encoding}}",
+          "-",
+          "{{outfile}}"
+        ]
+        timeout = "2 minutes"
+      }
+      working-dir = ${java.io.tmpdir}"/docspell-weasyprint"
     }
 
     # To convert image files to PDF files, tesseract is used. This