Aggregation over custom tags

[kiyose]

The CUR has within it columns for custom tags. We use these tags for billing annotation. It would be good for us to be able to pull metrics on resource utilization and cost based on these tags.

I could easily see this as a whitelist of tags in the config. eg:

customTags = [billto, product, costcenter]

Each tag would lead to a new metric dimension for each of the existing metrics.

Thank you for considering.