Add `sort_by` to the public API

[macumber]

Internally the BCL seems to be using sort_by = [{"version_modified.keyword": "desc"}, {"release_tag": "desc"}] in all of its results. For users of the page index method, it would be helpful to specify the sort criteria in the query, e.g. sort by name. Otherwise, the user has to query all of the results and then sort themselves.