feat: add Webhook Deliveries query type - #798

What

• Adds a Webhook Deliveries query type that lists deliveries of an organization or repository webhook, one row per delivery: delivered_at, event, action, status, status_code, duration, redelivery, repository_id, installation_id, and a derived success boolean.
• Query options: hook ID (required), event filter, and a status filter (All / Success / Failure). Leaving the repository empty queries an organization webhook; setting it queries that repository's webhook.
• Wraps Organizations.ListHookDeliveries and Repositories.ListHookDeliveries from go-github, alongside the existing REST-backed query types.
• Documents the query type in docs/sources/query-editor.md, including the required admin:org_hook / admin:repo_hook token scope and GitHub's 3-day delivery retention.

Why

• Closes Monitor GitHub Webhook Delivery Failures & Success Rates #488. Teams that rely on webhooks for automation currently have no way to notice when delivery silently starts failing. One row per delivery lets a dashboard compute success rates, chart failures over time, and alert on a failure threshold with ordinary transformations, so no separate aggregation query type is needed.

Notes for reviewers

• The deliveries endpoint has no server-side time filter and is cursor paginated, so the query pages from the most recent delivery until it reaches the start of the time range, capped at 50 pages (5000 deliveries) to protect the rate limit. Results that do not cover the whole time range carry a warning notice on the frame, either because that cap was reached or because GitHub ran out of deliveries within its 3-day retention window — a silently short window would understate failure counts.
• Because paging always starts at the most recent delivery, a time range that ends in the past still pages through everything that happened since. The API offers no way to avoid this.
• Deliveries include repository_id but no repository name; resolving names would cost an extra request per repository, so the ID is emitted as-is and documented.
• Deliveries that never got a response (timeout, DNS) have no status code and count as failures.

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