feat: Add ICMP, DNS, and GraphQL monitor types

Add three new monitor types with full support:

- ICMP: Ping monitoring with configurable packet count, tracks packet
  loss and average RTT. Marks degraded on partial packet loss.

- DNS: DNS resolution monitoring supporting A, AAAA, CNAME, MX, and TXT
  records. Optional custom DNS server and validation of expected IPs/CNAME.

- GraphQL: GraphQL endpoint monitoring with query execution, variable
  support, error detection, and content validation.

All new monitors include retry support, response time tracking, and
integrate with existing display options (round_response_time, etc).

GraphQL monitors also support SSL certificate tracking.

1 files changed, 61 insertions, 2 deletions

diff --git a/config.example.yaml b/config.example.yaml
index 18e9dbc..383c0b4 100644
--- a/config.example.yaml
+++ b/config.example.yaml
@@ -115,6 +115,44 @@ groups:
         verify_ssl: false                # Often false for self-signed certs in Geminispace
         # hide_ssl_days: false           # Gemini also tracks TLS certificate expiration
 
+  - name: "Advanced Monitoring"
+    monitors:
+      - name: "Server Ping"
+        type: icmp
+        target: "8.8.8.8"              # IP address or hostname
+        interval: 30s
+        timeout: 5s
+        # ping_count: 4                # Number of ICMP packets to send (default: 4)
+
+      - name: "DNS Resolution"
+        type: dns
+        target: "example.com"          # Domain to resolve
+        interval: 60s
+        timeout: 5s
+        # record_type: "A"             # DNS record type: A, AAAA, CNAME, MX, TXT (default: A)
+        # dns_server: "8.8.8.8:53"     # Custom DNS server (default: system resolver)
+        # expected_ips:                # Expected IP addresses (optional)
+        #   - "93.184.216.34"
+        # expected_cname: "example.com." # Expected CNAME record (for CNAME queries)
+
+      - name: "GraphQL API"
+        type: graphql
+        target: "https://api.example.com/graphql"
+        interval: 30s
+        timeout: 10s
+        graphql_query: |
+          query HealthCheck {
+            health {
+              status
+            }
+          }
+        # graphql_variables:           # Query variables (optional)
+        #   limit: "10"
+        expected_status: 200
+        # expected_content: '"status":"ok"' # Check response contains text
+        # headers:
+        #   Authorization: "Bearer token"
+
 # Incidents and maintenance (optional)
 incidents:
   # Scheduled maintenance example
@@ -157,8 +195,8 @@ incidents:
 #
 # Common fields for all monitor types:
 #   name: string (required)      - Display name for the monitor
-#   type: string (required)      - Monitor type: http, https, tcp, or gemini
-#   target: string (required)    - URL or host:port to monitor
+#   type: string (required)      - Monitor type: http, https, tcp, gemini, icmp, dns, or graphql
+#   target: string (required)    - URL, host:port, IP address, or domain to monitor
 #   interval: duration           - Check interval (default: 30s, or group default)
 #   timeout: duration            - Request timeout (default: 10s, or group default)
 #   retries: int                 - Number of retry attempts before marking as down (default: 0, or group default)
@@ -189,6 +227,27 @@ incidents:
 # TCP specific fields:
 #   (none - just needs host:port target)
 #
+# ICMP specific fields:
+#   target: string               - IP address or hostname to ping
+#   ping_count: int              - Number of ICMP packets to send (default: 4)
+#   Note: May require elevated privileges on some systems
+#
+# DNS specific fields:
+#   target: string               - Domain name to resolve
+#   record_type: string          - DNS record type: A, AAAA, CNAME, MX, TXT (default: A)
+#   dns_server: string           - Custom DNS server host:port (default: system resolver)
+#   expected_ips: []string       - Expected IP addresses to validate (optional)
+#   expected_cname: string       - Expected CNAME record to validate (optional)
+#
+# GraphQL specific fields:
+#   target: string (required)    - GraphQL endpoint URL
+#   graphql_query: string (required) - GraphQL query to execute
+#   graphql_variables: map       - Query variables (optional)
+#   expected_status: int         - Expected HTTP status code (default: 200)
+#   expected_content: string     - Text that must be present in response (optional)
+#   headers: map[string]string   - Custom headers (e.g., Authorization)
+#   verify_ssl: bool             - Verify SSL certificate (default: true)
+#
 # Duration format:
 #   Use Go duration strings: 30s, 1m, 5m, 1h, etc.
 #