Add an script to unzip `datadir` files when upgrading sbws to a version including #40017

Deploying 7430b4ef in longclaw, i realized that i had to manually unzip the files in datadir that were still not older than 28 days ago, cause sbws already zipped them, as the previous default was to zip them after 10 days.

When the bwauths will update to a version with this patch, it'd be convenient they run this script before so that we don't need to wait other 28 - 10 days to see the effects of the new version.