dashboards updated to account for null missing values

dashboards updated to account for null missing values

Prior to this change the charts had "Display/Null Value" set as null - but in
an environment where observations/metrics are arriving late or miss, the
 resulting chart would be part populated at best, at worst blank with only
 hover only providing an indication that data points are present.

Ideally the data should be present - but by setting as connected, null values
will not stop the graphs from being rendered.