Create a tagMetric field for divisor (to support 4cpu-hours UOM)

Currrently, we have a divisor of 4 that is used when submitting redhat.com:openshift_dedicated:4cpu_hour to Red Hat marketplace. In order to support this in a more re-usable way, introduce a `billingUomFactor` (feel free to find a better/shorter name).

Then set the tagMetric billingUomFactor to 0.25 for redhat.com:openshift_dedicated:4cpu_hour.

In src/main/java/org/candlepin/subscriptions/rhmarketplace/RhMarketplacePayloadMapper.java, replace the hardcoded metric divide by 4 with a multiply by the given metric's billingUomFactor (default to 1.0), and apply to all metrics.

For future-proofing, also implement billingUomFactor into the swatch-producer-aws