…ation

Fixes CRAFT-8

Remove redundant manual retry loop since @octokit/plugin-retry already
handles 5xx retries automatically (up to 3 times with exponential backoff).

The actual issue was missing response validation - GitHub GraphQL can return
HTTP 200 with missing/null repository field, causing TypeError when accessing
.repository properties.

Changes:
- Remove 37 lines of manual retry logic (duplicate of plugin behavior)
- Keep essential response validation with ?.repository check
- Maintain graceful error handling for all failure scenarios

This fixes three scenarios:
1. HTTP 502 errors: Handled by @octokit/plugin-retry
2. HTTP 200 with errors array: Caught by try-catch
3. HTTP 200 with missing repository: Caught by validation check

Capture GraphQL changelog failures to Sentry with rich context for monitoring:
- Tag 'error_type' for easy filtering (graphql_changelog_failure)
- Tags for chunk_number and total_chunks for tracking failure patterns
- Context with chunk details, commit count, HTTP status, and error name

This enables:
- Tracking frequency of GraphQL failures in production
- Identifying patterns (e.g., specific chunks that fail consistently)
- Monitoring the effectiveness of the retry plugin
- Better visibility into GitHub API reliability issues

The error is still logged as a warning and handled gracefully (skipping
the failed chunk and continuing with remaining commits).

Move GraphQL query into the main graphql_chunk context and remove the
redundant queryLength metric. The query string itself is more useful for
debugging, and totalHashes already provides the scale information needed.