Remove label value sanitization in prometheus output (#2939)

plugins/outputs/prometheus_client/prometheus_client.go

@@ -205,7 +205,7 @@ func (p *PrometheusClient) Write(metrics []telegraf.Metric) error {
 
 		labels := make(map[string]string)
 		for k, v := range tags {
-			labels[sanitize(k)] = sanitize(v)
+			labels[sanitize(k)] = v
 		}
 
 		for fn, fv := range point.Fields() {

plugins/outputs/prometheus_client/prometheus_client_test.go

@@ -144,7 +144,7 @@ func TestWrite_Sanitize(t *testing.T) {
 	require.True(t, ok)
 
 	require.Equal(t, map[string]string{
-		"tag_with_dash": "localhost_local"}, sample1.Labels)
+		"tag_with_dash": "localhost.local"}, sample1.Labels)
 }
 
 func TestWrite_Gauge(t *testing.T) {