Add 'cardinality' dimension to the emited telemetry data

### Context

We are planning to employ sampling of telemetry data. Over time there will be ability to tune the sampling or/and control it more granularly based on source type or measured population.
In order to properly interpret the data when reviewing in backend - we need to know what sample size does the data represent.

### Suggested implementation

Add 'Cardinality' property that will be storing the acutal sampling rate used at the time of collection.