Add a new DNS monitor type that periodically queries DNS records and tracks two key metrics

[gorkem-bwl]

Users want to monitor whether their domains are resolving correctly and how fast DNS responses are. This complements existing HTTP and ping monitors by catching DNS-level issues that may not surface through higher-level checks.

Add a new DNS monitor type that periodically queries DNS records and tracks two key metrics:

1. Query time: The time it takes for a DNS query to resolve (similar to ping/HTTP response time). This can be visualized as a graph on the monitor details page, consistent with how we display response times for other monitor types.
2. Query status: Whether the DNS record is resolving successfully or not. This enables uptime/downtime tracking for DNS resolution, triggering incidents when a domain stops resolving.

• Use a DNS library (e.g., Node.js dns.resolve) to perform lookups
• Support configurable DNS server (e.g., 8.8.8.8, 1.1.1.1, or custom)
• Support common record types (A, AAAA, CNAME, MX, TXT, NS)
• Track query time in milliseconds and resolution success/failure
• Integrate with existing incident and notification systems