Handle metering for ROSA hosted control plane

Subscription Watch should handle the metering for ROSA clusters with hosted control plane. The metering will be based on two different metrics - the number of clusters and the number of vCPUs across all clusters of type ROSA hosted control plane.

AMS will send subscription labels to telemetry that will provide product (cluster type) information for the clusters as well as the billing account ID (AWS account ID) used for the subscription billing. The work and specifics for the subscription label is going to be captured in SDB-3085.

Swatch will additionally need to support pre-purchase amounts based on contracts that customers can buy. The usage within contract limits will need to be tracked with Swatch and only overages will be submitted to AWS. The contract information will be captured and stored by the RHIT service based on SNS notifications received from AWS (work captured in ITPART-393). The contract details are then made available through an API (jira story to be linked here once its created). separate card being need to pull the contract information from RHIT backend to determine overages.

The metering in Swatch will follow option 3 (slide 23: https://docs.google.com/presentation/d/1DwtbXpzWmJgRn2ZVdwhLFk5tvdM-xvHoAnIZ72_LiOA/edit#slide=id.g540d45e6e6_4_44) to ensure the most flexibility for customers. The usage will be aggregated at the monthly level and compared against the contract amount for calculating overages.

The contract quantities will be specified as concurrent clusters and worker node capacity (vCPUs). Hence, the contract amount will need to be converted to a metric*hour unit by multiplying the contract amount by the number of hours in a month (730?). Similarly, the usage will need to be calculated in metric*hour units.

Question: What is the lowest granularity that Swatch can support for metering and submitting usage to AWS? Is it an hour, or 30 min or 15 min or lower?

See https://docs.google.com/document/d/1oYrj2tXJ91EEjOQBTfY9jcdSc-D_WEo64efKwOj897g/ for detailed user scenarios/flows.

Key differences for ROSA hosted control plane billing:

 - AWS seller account is different from that used for other marketplace offerings

 - Contracts need to be considered and overages calculated based on that