ref https://linear.app/tryghost/issue/CFR-31/
- when relations were included, erroneous logic resulted in the model's
default sort being applied
- the model default sort is not intended for the content API and
needlessly slowed down responses
- there's a change for users here that should be incredibly unlikely to
be hit; default sort is `published_at desc` which will be secondarily
sorted by `id desc` instead of `published_at desc, updated_at desc, id
desc`
This is a very significant performance improvement for content API
requests with includes for sites with a significant amount of data,
which will primarily impact those using Ghost as a CMS or theme {{#get}}
helpers.
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