Update Functions Metadata API to return WebHook URI info

Currently the invoke_url_template info returned by the functions metadata APIs only returns a URI for http functions.

We should also return the invoke URI for functions based on extensions that use WebHook dispatch (e.g. EventGrid).

Start by tracing the Functions metadata APIs that populate invoke_url_template and inspect how extensions using WebHook dispatch, such as EventGrid, provide their invoke URI. Done means metadata responses include that URI for WebHook-based functions while preserving the existing HTTP-function behavior; exercise both response paths through the metadata API.

Written by the indexing model from the issue text.