This is the top-level task for deploying [GlobalWatchlist](https://www.mediawiki.org/wiki/Extension:GlobalWatchlist), and extension developed as part of a [grant from the WMF](https://meta.wikimedia.org/wiki/Grants:Project/DannyS712/Create_a_global_watchlist_extension)
[] Add the new extension submodule to the git mediawiki/extensions repo
[] Security review ({T260466})
[] Move extension CI config to wikimedia-deployed section
[] Add extension to the make-wmf-branch release tool
[] Deploy to beta cluster
[] Add to `extension-list`
[] Add config `$wmgUseGlobalWatchlist` to `InitialiseSettings.php`, defaulting to false
[] In `CommonSettings.php`, load the extension when `$wmgUseGlobalWatchlist` is true
[] In `InitialiseSettings-labs.php`, set `$wmgUseGlobalWatchlist` to true for beta metawiki
[] Performance review ({T260860})
[] In `InitialiseSettings.php`, set `$wmgUseGlobalWatchlist` to true for metawiki
[] Update https://www.mediawiki.org/wiki/Extension:GlobalWatchlist ("Release status" etc)