fix failed_spans typo in grafana dashboards (#1465)

Co-authored-by: Austin Parker <austin@ap2.io>

Author: edhjer

kubernetes/opentelemetry-demo.yaml

@@ -3214,7 +3214,7 @@ data:
             "type": "prometheus",
             "uid": "webstore-metrics"
           },
-          "description": "Sent by Exporter\notelcol_exporter_send_failed_spans",
+          "description": "Sent by Exporter\notelcol_exporter_send_failed_metric_points",
           "fieldConfig": {
             "defaults": {
               "color": {

src/grafana/provisioning/dashboards/demo/opentelemetry-collector-data-flow.json

@@ -1734,7 +1734,7 @@
         "type": "prometheus",
         "uid": "webstore-metrics"
       },
-      "description": "Sent by Exporter\notelcol_exporter_send_failed_spans",
+      "description": "Sent by Exporter\notelcol_exporter_send_failed_metric_points",
       "fieldConfig": {
         "defaults": {
           "color": {