Add documentation on enabling Microsoft.Insights for Azure Events / Metrics

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The Microsoft.Insights resource provider is required for ManageIQ Events and Metrics features to be able to work with an Azure cloud provider.

Without this resource provider enabled events / metrics will be disabled.

This has always been a requirement for azure events/metrics, we had a talk article from a community member about how to enable this resource provider but this doesn't appear to be viewable any longer https://talk.manageiq.org/t/how-can-i-see-azure-utilization/5298/4 It doesn't seem like instructions on this being a requirement, or how to enable it ever made it to the documentation.