chore(release): Prepare for 2.15.0 release

[mejo-]

✨New

• ⭐ Add support for page favorites. (Favourite pages #300)
• 🔧 Add console function to debug sync/Yjs issues.

🐛Fixes

• 🖨️ Several print style fixes. ([printing] Collective title on blank first page (Firefox only?) #1110)
• 💄 Make page list header, landing page and trash sticky again. (Page trash no longer sticky #1523)
• ⌛ Update timestamp in page info bar when page gets saves via "Done" button. ("Last changed by" does not update after edit, only after page reload #1371)
• 💄 Fix alignment of landing page widgets.
• 🐎 Use storage id for performant index usage on dashboard query.
• 🏛️ Add return types of storage wrapper.
• 👷 Exclude rector.php from release tarball. (Don't ship rector.php? #1541)
• 🔗 Fix page link in reference widgets for index pages.
• 🔗 Preserve anchors in links of reference widgets. Thanks @Koc.
• 🐛 Create index page if subfolders contain pages.

🌎Translations

• 🗣️ Translation updates from Transifex. Thanks to all contributors.

🚧Updates & Tooling

• ⬆️ Update NPM dependencies.
• ⬆️ Update PHP composer dependencies.

🏁 Checklist

• Code is properly formatted (npm run lint / npm run stylelint / composer run cs:check)
• Sign-off message is added to all commits
• Documentation (README or documentation) has been updated or is not required