Add move-pages script

[benface]

This is a follow-up to #838. I realized that while the fix-pages-structure script was super useful when adding or deleting pages, moving pages was still a pain because if you only did it in English and then ran fix-pages-structure, it would delete the translated pages at the old paths (because those paths no longer exist in English) and then copy the English pages to the new paths, thus reverting all translations to English until Crowdin synced and the next Crowdin PR was merged. So I created a move-pages script that moves (or simply renames) a page (or a directory of pages) across all languages/locales:

Usage: pnpm run move-pages <source-path> <destination>
Examples:
  pnpm run move-pages page.mdx new-directory             Move page (keeping name)
  pnpm run move-pages page.mdx new-name.mdx              Rename page
  pnpm run move-pages page.mdx new-dir/new-name.mdx      Move and rename page
  pnpm run move-pages developing subgraphs/developing    Move directory
  pnpm run move-pages developing subgraphs               Rename directory