On one of our capacity dashboards I would like to be able to include The CPU Demand or Workload Average over a 30 day period in the .xml file that I am using to display specific data on the dashboard. If there is a metric attribute key for this, I can't find it. I want to be able to do this from the cluster level, not an individual VM. Does this attribute key exist?
If not, any ideas on how I could create a Super Metric that could average load over 30 days?
The key does not exist, because it is not a metric. You're looking for a simple moving avg of the data, and you'd get this by using a View to do a 'avg' transformation on those metrics over your desired period of time. SMs cannot do simple moving averages, and you'd need to use a View.
following up what Mark said you will need to create a view. Instructions on how to do this can be found here
vROPs 6 – Creating an Advance view with Average, Maximum, and Summary features | VM IGNITE