storage,ac: determine provisioned iops/bandwidth from instance metadata

Cloud providers provide an internal instance metadata API so that from within a VM one can query metadata about the instance. See https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/ec2-instance-metadata.html

It might be possible to automatically determine the provisioned iops and bandwidth for a store's disk using this API and mapping it to a store path. Customers don't tend to use the CLI flag to explicitly tell us the provisioned bandwidth of the drive, so inferring it within cloud environments could in practice improve admission control's ability to regulate disk traffic.

Jira issue: CRDB-50462