Add Type to api.Feature

[jameshartig]

Describe the feature request

The API returns the type of the feature. It should be added as a struct field on api.Feature.

Background

We will have some special metrics around kill-switch type features to specifically track when those are being enabled to kill features.

Solution suggestions

Add Type string field to api.Feature.

[jameshartig]

@FredrikOseberg this one was simple enough that I just opened a PR. There's a bigger discussion around ease of getting to the *api.Feature but I believe we have a workaround internally that doesn't involve any change to the client.