DrDroid AI: ** Add: GithubAppSourceMetadataExtractor for GitHub App authentication

[sidPhoenix17]

**

Summary

Added new GithubAppSourceMetadataExtractor class to support GitHub App authentication with app_id, private_key, and installation_id parameters.

Changes

• Created github_app_metadata_extractor.py with GithubAppSourceMetadataExtractor class
• Implemented extract_repos() and extract_members() methods using GithubAppAPIProcessor
• Updated init.py to export the new class

Testing

• Verified Python syntax is valid
• Confirmed class structure matches GithubSourceMetadataExtractor pattern
• Validated proper integration with GithubAppAPIProcessor

This PR is created as part of investigation https://aiops.drdroid.io/?investigation_id=3c1f69dc-1b1f-4e57-a77e-e8359dee9410