feat: Add generic `Kubeflow Application Workloads State` grafana dashboard

[orfeas-k]

The implementation was modified from what was specced. I can update the spec once the review gives a +1 too. Details for the final dashboard are in https://github.com/canonical/bundle-kubeflow/issues/877#issuecomment-2072060824.

• Implement a generic grafana dashboard that shows the state (up or down) of all CKF charms that provide metrics.
• Fetch grafana dashboard library and implement a GrafanaDashboardProvider.

Closes canonical/bundle-kubeflow#877

Testing

This is how the dashboard looks like:

If you 'd like to test the COS integration and see the dashboard yourself, then follow the CKF - COS integration guide.

[orfeas-k]

Updated from all the comments and discussions. Here's a screenshot of how the updated wording looks like:

This is to reflect that a charm may be misconfigured and e.g. Blocked, so its application workload won't be functioning properly. However, it will still run and provide metrics.