TUN-8441: Correct UDP total sessions metric to a counter and add new ICMP metrics

cloudflared_udp_total_sessions was incorrectly a gauge when it
represents the total since the cloudflared process started and will
only ever increase.

Additionally adds new ICMP metrics for requests and replies.

datagramsession/metrics.go

@@ -15,7 +15,7 @@ var (
 		Name:      "active_sessions",
 		Help:      "Concurrent count of UDP sessions that are being proxied to any origin",
 	})
-	totalUDPSessions = prometheus.NewGauge(prometheus.GaugeOpts{
+	totalUDPSessions = prometheus.NewCounter(prometheus.CounterOpts{
 		Namespace: namespace,
 		Subsystem: "udp",
 		Name:      "total_sessions",

ingress/icmp_metrics.go

@@ -0,0 +1,39 @@
+package ingress
+
+import (
+	"github.com/prometheus/client_golang/prometheus"
+)
+
+const (
+	namespace = "cloudflared"
+)
+
+var (
+	icmpRequests = prometheus.NewCounter(prometheus.CounterOpts{
+		Namespace: namespace,
+		Subsystem: "icmp",
+		Name:      "total_requests",
+		Help:      "Total count of ICMP requests that have been proxied to any origin",
+	})
+	icmpReplies = prometheus.NewCounter(prometheus.CounterOpts{
+		Namespace: namespace,
+		Subsystem: "icmp",
+		Name:      "total_replies",
+		Help:      "Total count of ICMP replies that have been proxied from any origin",
+	})
+)
+
+func init() {
+	prometheus.MustRegister(
+		icmpRequests,
+		icmpReplies,
+	)
+}
+
+func incrementICMPRequest() {
+	icmpRequests.Inc()
+}
+
+func incrementICMPReply() {
+	icmpReplies.Inc()
+}

ingress/origin_icmp_proxy.go

@@ -105,6 +105,7 @@ func isEchoReply(msg *icmp.Message) bool {
 }
 
 func observeICMPRequest(logger *zerolog.Logger, span trace.Span, src string, dst string, echoID int, seq int) {
+	incrementICMPRequest()
 	logger.Debug().
 		Str("src", src).
 		Str("dst", dst).
@@ -118,6 +119,7 @@ func observeICMPRequest(logger *zerolog.Logger, span trace.Span, src string, dst
 }
 
 func observeICMPReply(logger *zerolog.Logger, span trace.Span, dst string, echoID int, seq int) {
+	incrementICMPReply()
 	logger.Debug().Str("dst", dst).Int("echoID", echoID).Int("seq", seq).Msg("Sent ICMP reply to edge")
 	span.SetAttributes(
 		attribute.String("dst", dst),