Improve FAQ

[killme2008]

⏺ Most Critical Missing Questions to Add:

High Priority (Should Add)

1. "How do I migrate from Prometheus to GreptimeDB?" - Most common migration path
2. "What's the recommended sizing for my workload?" - Critical for planning
3. "How do I backup and restore my data?" - Essential operational concern
4. "How do I optimize query performance?" - Common performance issue
5. "Can I use my existing Grafana dashboards?" - Integration concern

Medium Priority (Nice to Have)

1. "How do I handle high cardinality data effectively?" - Performance optimization
2. "What monitoring should I set up for GreptimeDB itself?" - Operational best practice
3. "How do I upgrade GreptimeDB without downtime?" - Production concern
4. "What are the best practices for schema design?" - Data modeling guidance
5. "How do I set up alerting with GreptimeDB?" - Common integration need