Import a dashboard w/ a defined dashboard ID

[Robert Gildein]

When I tried to import a new dashboard that contained a defined ID (e.g. id=1)
I got the following error:

```bash
unit-grafana-0: 14:31:02 ERROR unit.grafana/0.juju-log dashboards:40: import_dashboard None failed: Error importing dashboard "[juju-prometheus-bind-exporter] Bind designate-bind": {"message":"Dashboard not found","status":"not-found"}
```

After a long search, I found out that it is due to the fact that in the
template, which I developed in Grafan UI and then exported it, there is
a defined id=1, but the dashboard under such an id was no longer in Grafan.

I think this should be addressed, either by checking whether the dashboard
with the given id does not exist or the error message could explicitly say
that this is an error from Grafan's response.

[Eric Chen (eric-chen)]

This charm is no longer being actively maintained. Please consider using the new Canonical Observability Stack instead.
(https://charmhub.io/topics/canonical-observability-stack)
I will close this issue