docs: add image optimization engines to the PDF Engines config table

Author: gulien

docs/configuration.mdx

@@ -287,6 +287,7 @@ The following flags allow you to configure the PDF Engines module:
 | <span class="badge badge--secondary">--pdfengines-split-engines</span>           | <span class="badge badge--secondary">PDFENGINES_SPLIT_ENGINES</span>           | Set the PDF engines and their order for the split feature - empty means all.               | pdfcpu,qpdf,pdftk     |
 | <span class="badge badge--secondary">--pdfengines-flatten-engines</span>         | <span class="badge badge--secondary">PDFENGINES_FLATTEN_ENGINES</span>         | Set the PDF engines and their order for the flatten feature - empty means all.             | qpdf                  |
 | <span class="badge badge--secondary">--pdfengines-convert-engines</span>         | <span class="badge badge--secondary">PDFENGINES_CONVERT_ENGINES</span>         | Set the PDF engines and their order for the convert feature - empty means all.             | libreoffice-pdfengine |
+| <span class="badge badge--secondary">--pdfengines-optimize-images-engines</span> | <span class="badge badge--secondary">PDFENGINES_OPTIMIZE_IMAGES_ENGINES</span> | Set the PDF engines and their order for the image optimization feature - empty means all.  | pdfcpu                |
 | <span class="badge badge--secondary">--pdfengines-read-metadata-engines</span>   | <span class="badge badge--secondary">PDFENGINES_READ_METADATA_ENGINES</span>   | Set the PDF engines and their order for the read metadata feature - empty means all.       | exiftool              |
 | <span class="badge badge--secondary">--pdfengines-write-metadata-engines</span>  | <span class="badge badge--secondary">PDFENGINES_WRITE_METADATA_ENGINES</span>  | Set the PDF engines and their order for the write metadata feature - empty means all.      | exiftool              |
 | <span class="badge badge--secondary">--pdfengines-encrypt-engines</span>         | <span class="badge badge--secondary">PDFENGINES_ENCRYPT_ENGINES</span>         | Set the PDF engines and their order for the password protection feature - empty means all. | qpdf,pdftk,pdfcpu     |