Update troubleshooting.md - Grafana dashboard link (open-telemetry#8133)

Updated Grafana dashboard link. Old dashboard was not updated for
3+years. I linked "my" dashboard, which is published also in the
[repo](https://github.com/monitoringartist/opentelemetry-collector-monitoring),
so users may contribute and improve it easily.

Dashboard has structure - horizontal by receivers/processors/exporters,
vertical by traces/metrics/logs + process metrics. It is trying to be
generic, no distro/component specific.

docs/troubleshooting.md

@@ -56,8 +56,8 @@ more details.
 $ otelcol --metrics-addr 0.0.0.0:8888
 ```
 
-A grafana dashboard for these metrics can be found
-[here](https://grafana.com/grafana/dashboards/11575).
+A Grafana dashboard for these metrics can be found
+[here](https://grafana.com/grafana/dashboards/15983-opentelemetry-collector/).
 
 Also note that a Collector can be configured to scrape its own metrics and send
 it through configured pipelines. For example: