Publish disk prices

Register your own block storage rates so CostGraph can price volumes it has no public price for. An entry is upserted on its natural key (provider, service, region, availability zone, usage type, type and period billing hours), so re-posting the same entry with a new cost keeps its id and reprices everything already using it. The returned id is what you attach to a volume with the costgraph.ai/pricing-id.disk label or tag.