This reduces chances of errors where consumers of strings mutate inputs
and reduces memory usage of the app.
Test suite passes now, but there may be some stuff left, so we will run
a few sites on a branch prior to merging
The wizard searches for:
* a topic that with the "is_welcome_topic" custom field
* a topic with the correct slug for the current default locale
* a topic with the correct slug for the English locale
* the oldest globally pinned topic
It gives up if it didn't find any of the above.
