Sort checkout nodes by newest first in API response

[padovan]

When fetching data from https://kernelci-api.westus3.cloudapp.azure.com/latest/nodes?data.kernel_revision.tree=mainline&kind=checkout we get oldest checkout first, forcing the user to keep pulling pages in.

It would be great to order data by newest first on the server side.

ref:

kernelci-api/api/db.py

Line 167 in a62d03f

def _prepare_query(self, attributes):