Long-term goal: synchronize all outdated pages

Hey localization folks! Now that we have finished formatting all of the localized content using Prettier, and have purged a significant amount of untranslated files, I feel that it is now time for us to tackle the next phase of cleanup. This is one that will require the assistance of all localization teams, and all the help we can get.

For this phase, I would love for us to focus on updating outdated translations, so that we can improve the quality of translated content rapidly. This involves checking how in-sync each page is with upstream and updating the translation as needed.

In my opinion, I think that the priority of documents should be the following:

• Writing guidelines pages (see #14373)
• Community guidelines pages (/MDN/Community)
• Partially translated pages
• Pages untouched since the wiki migration
• Pages without a sourceCommit front matter key set

Once a page has been updated, it is important that we add the sourceCommit front matter key so that we can keep track of the staleness of the document in the future and programmatically determine which translations are most outdated. Eventually, we should get to a point where every translated document has a sourceCommit key and we can require it in the schema.