Sort supplier_frameworks in ascending order of date returned
Sort supplier_frameworks in ascending order of date returned

Currently the ordering of supplier_frameworks in the API response is not defined, so we reorder the response from oldest to newest returned agreement.  Our datetime format sorts in lexicographical order, so there is no need to eplicitly cast the `agreementReturnedAt` values to `datetime` objects before sorting.

alphagov/digitalmarketplace-admin-frontend,alphagov/digitalmarketplace-admin-frontend,alphagov/digitalmarketplace-admin-frontend,alphagov/digitalmarketplace-admin-frontend