feat: add GitLab metadata enrichment to migrated issues

[mordonez]

Summary

This PR adds support for enriching migrated issues with GitLab-specific metadata. When enabled, the migration tool will extract and format GitLab metadata (weight, time tracking, due date, health status) and append it to issue descriptions on GitHub.

Changes

• New feature: GitLab metadata extraction and formatting

  • Extract weight, time estimates/spent, due date, and health status from GitLab issues
  • Format metadata as a clean markdown section appended to issue descriptions

• Automatic weight label creation:

  • Create weight labels (e.g., "weight::5") on GitHub with consistent color (#d1d5da)
  • Gracefully handle existing labels (422 status)

• New settings:

  • enrichGitLabMetadata: Enable/disable metadata enrichment (default: false)
  • createWeightLabels: Auto-create weight labels on GitHub (default: false)

• Helper functions in src/utils.ts:

  • extractGitLabMetadata(): Extract metadata from GitLab issues
  • formatGitLabMetadata(): Format metadata as markdown
  • ensureWeightLabel(): Create weight labels on GitHub

Benefits

• Preserves important GitLab context during migration
• Makes migrated issues more informative with time tracking and weight data
• No breaking changes - fully backward compatible
• Opt-in feature via settings

Testing

Tested with TypeScript 3.9.6 compilation and runtime verification.

Example Output

Migrated issues will have a footer section like:

---
**Migrated from GitLab**
- ⏱️ Time Estimate: 2h
- ⏲️ Time Spent: 1h 30m
- ⚖️ Weight: 5
- 📅 Due Date: 2024-12-31
- 🏥 Health: on_track