Manage elastic rules separately

[egibs]

This PR adds the elastic rules as a separate third-party source.

This language has been cited for recent changes to upstream rules we pull from:

You may not provide the software to third parties as a hosted or managed
service, where the service provides users with access to any substantial set of
the features or functionality of the software.

I believe the upstream rules were being used in a managed service which conflicts with the language, but malcontent is neither hosted nor managed and is entirely copy-left.