Updated Grafana Dashboard

Fixed tooltips and crosshairs of all graphs.

A new cluster overview section at the top that features:
* Base backup information
* Last archived WAL
* 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

Improved Server Health section
* 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 parameter section to make it more readible.

Added volume space and inode usage gauges.

Signed-off-by: Itay Grudev <itay+github.com@grudev.com>
Signed-off-by: Itay Grudev <igrudev@clustermarket.com>
Signed-off-by: Itay Grudev <itay+git2020@grudev.com>
Signed-off-by: Itay Grudev <igrudev@clustermarket.com>