How to use kops addons

Can't seem to find the documentation on how to use kops' addons (found in kops/addons) ; more specifically `logging-elasticsearch`.

It seems I could just apply the YML config via `kubectl` but what is that "channel" tool mentioned [here](https://github.com/kubernetes/kops/blob/master/docs/addon_manager.md)?

Thanks!

Start with docs/addon_manager.md and the kops/addons directory, focusing on logging-elasticsearch and the referenced channel tool. Document how to use the addon, including whether kubectl application is sufficient and what channel does; done means the usage path is clear to users.

Written by the indexing model from the issue text.