Add multi-tool workflow server instructions specific to local GitHub MCP

[mattdholloway]

This pull request adds new server instructions by introducing scenario-based instructions for common development tasks. These improvements help users understand which GitHub toolsets and API endpoints to use for typical workflows, making the instructions more actionable and context-aware.

An example of this is as follows, using the Triaging Security Alerts scenario with the following instruction:

Use list_dependabot_alerts, list_code_scanning_alerts, or list_secret_scanning_alerts with state='open' to find active security issues. Use get_*_alert for detailed information about specific alerts. For broader context, search list_global_security_advisories or get_global_security_advisory for known CVEs affecting your dependencies.

Closes: