Endpoint support

This is to go along with https://github.com/my-koop/service.website/pull/186. I added a couple of example endpoints (although not used here) to show what's possible. These will be moved to https://github.com/my-koop/module.base shortly.

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So this does guarantee that `res` exists at all times when `err` happens? In our case I think this might be false, if `actions.inventory.list` were to expect query data (when using `:wildcards`) and didn't provide it.