Add Support for Sobelow (Elixir)

We've been using Salus for awhile now at my current company and have integrated [Sobelow](https://github.com/nccgroup/sobelow) into it for the purposes of scanning Elixir code.

Our implementation is not ready for primetime via a PR and we're unsure if we have time to dedicate to cleaning up our fork so it's ready for a PR; so we'd love some assistance getting it integrated from official maintainers so we don't have to continue supporting our fork as it drifts further and further away from the main branch.