Add docs in metrics dictionary for object value type
We should document when the object type can be uses for a metric definition
For object type we should require a JSON schema and a data validation agains the linked JSON schema
Existing object types
When considering adding an objects type for metric in Usage Ping, consider answering to following questions
- Does data make sense all together only?
- Does data belong to same product category, group, stage?
- is data for the same time interval?