Sort checkout nodes by newest first in API response

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: https://github.com/kernelci/kernelci-api/blob/a62d03f4f15e30c8d9f9113833380cff0c25f14d/api/db.py#L167

Start in api/db.py around line 167 and trace the query serving the /latest/nodes endpoint with kind=checkout. Verify the API response and pagination for the linked request, and consider the work complete when newest checkout nodes are returned first.

Written by the indexing model from the issue text.