User story:
As an editor I want to have a reliable way to see all pages that use sub-references.
Acceptance criteria:
Implement a new tracking category like it was done in T239989: Use category rather than page prop to mark Book Referencing pages for the extends syntax.
Notes:
Inspiration for the i18n can be taken from the extends patch https://gerrit.wikimedia.org/r/c/mediawiki/extensions/Cite/+/775906