Add three new services covering labels, webhooks, and file content
operations. LabelService handles repo and org labels without Resource
embedding due to heterogeneous paths. WebhookService embeds Resource
for standard CRUD on repo hooks plus action methods for test delivery
and org hooks. ContentService provides file CRUD and raw file retrieval.
Adds GetRaw method to Client for non-JSON responses.
Co-Authored-By: Virgil <virgil@lethean.io>
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
