Add Microsoft Application Insights output plugin (#4010)

plugins/outputs/application_insights/transmitter.go

@@ -0,0 +1,19 @@
+package application_insights
+
+import "github.com/Microsoft/ApplicationInsights-Go/appinsights"
+
+type Transmitter struct {
+	client appinsights.TelemetryClient
+}
+
+func NewTransmitter(ikey string) *Transmitter {
+	return &Transmitter{client: appinsights.NewTelemetryClient(ikey)}
+}
+
+func (t *Transmitter) Track(telemetry appinsights.Telemetry) {
+	t.client.Track(telemetry)
+}
+
+func (t *Transmitter) Close() <-chan struct{} {
+	return t.client.Channel().Close(0)
+}