Grafana Dashboard Cluster Overview Improvements (cloudnative-pg#1916)

* Base backup and last archived WAL information
* Total CPU and memory usage across all nodes
* An Alerts section
* Last failover/switchover time
* Cluster PostgreSQL version
* Transactions per second
* Volume usage and total database size
* Replication/Write/Flush/Replay lag
* Added instance zone
* Displaying the full PostgreSQL version
* Bug Fix: When there are redundant `kube-state-metrics` instances there are duplicate status gauges
* Bug Fix: Max Connections not displaying a progress bar in the gauge due to missing `min` and `max` values.
* Transposed configuration section
* Added volume space and inode usage gauges.
* Fixed tooltips and set shared crosshairs of all graphs.
* Bug Fix: Cluster variable query picking up any metric ending with cluster

---------

Signed-off-by: Itay Grudev <igrudev@clustermarket.com>

docs/src/quickstart.md

@@ -321,6 +321,11 @@ kubectl apply -f \
 Which will be picked up by the Grafana page in a few seconds. You should now
 see the `CloudNativePG` dashboard.
 
+!!! Warning
+    Some graphs in the previous dashboard make use of metrics that are in alpha stage by the time
+    this was created, like `kubelet_volume_stats_available_bytes` and `kubelet_volume_stats_capacity_bytes`
+    producing some graphs to show `No data`.
+
 ![local grafana](images/grafana-local.png)
 
 Note that in our example setup, both Prometheus and Grafana will pick up