Describe a named label source

Returns the description of a named label source in JSON format. The label source name should be provided as part of the URL path after /labelSources/.

Resource dependencies: A named label source typically references a named table (see the table field, e.g. NamedTable) that provides the data used to generate labels. This referenced table must already exist in the repository for the label source to render or describe correctly.

Authorization: Requires EXECUTE permission on the requested label source. If the caller lacks permission, the API returns 403 Forbidden; if the label source does not exist, it returns 404 Not Found. Both share the same error code (DIS-MS-1016), but the distinct HTTP status and message text make the two cases distinguishable to the caller.