Add new admin API endpoints for dashboard metrics and system-wide
realtime statistics:
- Add /admin/dashboard/summary endpoint with aggregated metrics
including requests, tokens, latency, masters, keys, and provider
keys statistics with time period filtering
- Add /admin/realtime endpoint for system-level realtime stats
aggregated across all masters
- Add status filter parameter to ListAPIKeys endpoint
- Add hour grouping option to log stats aggregation
- Update OpenAPI documentation with new endpoints and schemas
