Publish compute prices

Register your own compute rates so CostGraph can price machines it has no public price for, such as bare metal or a private cloud. An entry is upserted on its natural key (provider, service, region, availability zone, usage type, instance type, operating system and period billing hours), so re-posting the same entry with a new cost keeps its id and reprices everything already using it. Changing any key field mints a new id, because it describes a different SKU. The returned id is what you attach to a resource with the costgraph.ai/pricing-id.compute label or tag.