[chore] Configure GitHub action to handle page migrations

[andrewnicols]

What do we need to do?

Suggestion after discussion with Eloy.

We already track a list of migrated pages in the migratedPages.js file.

At the moment we manually edit the legacy docs to add the Template link after an issue is merged.

What we could look to do is, for any page which has been migrated:

• use the WikiMedia API to set the {{Template:Migrated|newDocId=/path/to/new/doc}}
• Protect the page from further changes.

This would allow us to reduce steps in the migration, and would allow us to restructure pages in the new docs and have the Migration links continue to work.

The WikiMedia API should support these changes.

[andrewnicols]

Partially implemented in #62, but not yet protecting pages as we aren't ready to do this yet.

[andrewnicols]

This is now protecting pages since #111. Closing.