TUN-3375: Upgrade coredns and prometheus dependencies

vendor/github.com/opentracing/opentracing-go/ext.go

@@ -0,0 +1,24 @@
+package opentracing
+
+import (
+	"context"
+)
+
+// TracerContextWithSpanExtension is an extension interface that the
+// implementation of the Tracer interface may want to implement. It
+// allows to have some control over the go context when the
+// ContextWithSpan is invoked.
+//
+// The primary purpose of this extension are adapters from opentracing
+// API to some other tracing API.
+type TracerContextWithSpanExtension interface {
+	// ContextWithSpanHook gets called by the ContextWithSpan
+	// function, when the Tracer implementation also implements
+	// this interface. It allows to put extra information into the
+	// context and make it available to the callers of the
+	// ContextWithSpan.
+	//
+	// This hook is invoked before the ContextWithSpan function
+	// actually puts the span into the context.
+	ContextWithSpanHook(ctx context.Context, span Span) context.Context
+}