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
* Doing it in a post migration was a bad idea
because the migration will fail if the site
is down while trying to download uploads
which points to the instance. This mainly
affects self-hosters using `discourse_docker`
where `./launcher rebuild` will take the
existing container down.
