Publish generated Python and JS clients

SOLR-16835 and SOLR-17062 gave us the ability to generate Python and JavaScript clients from as a part of the Solr build. But while these clients are used in small ways for dog-fooding (e.g. in the Admin UI), we aren't yet publishing them in any way to make them available to users.

We should decide on a format for publishing these clients (a source code TGZ, pip/npm packages, something else?), and modify our release process to make both the JS and Python clients available in that format.