UI: kea main dashboard should contain critical info (pool util, HA status)

The reason to have all the critical information on the main dashboard is, the operator is going to have that screen up on the monitor all the time. The main way the operator will navigate to other screens is by clicking on something that looks wrong on the main dashboard. You can't monitor stuff effectively if it is not on the main screen, because you won't see the display showing an error or red icon or something.

@vicky will surely add more to this, but given her feedback (see Stork minutes from 2020-03-10), here are the things that should be listed on the Kea apps list:

• machine (links to details about the machine/os/cpu). may turn red if there is an alert such as CPU utilization threshold event.
• pool utilization (maybe show just the pool with highest utilization?)
• HA status
• HA: time since last failover event (not sure if the uptime counter would capture this or not).
• clicking on the HA status could navigate to a details window, which could show the HA partner, and info on the last or a few prior failover events, such as a time stamp, what triggered the FO, any other information we have.
• leases per second (this is intended as an average, say for the past 15 minutes) clicking on this could lead to Grafana for more historic detail
• uptime (clicking on this could lead to details of operational events, like software updates, reloads, configuration changes, )