Currently, in order to create a feature service webhook you either have to have the Admin role assigned and perform this action via the admin portal, or use the administrative API. This is a complicated multi-part process, and too cumbersome for this type of capability.
I'd recommend the feature service content owner be able to create and manage webhooks directly from the Settings tab of Feature Service item page. Or if this isn't feasible, some other GUI-based method that doesn't require API calls.
