Add 'cardinality' dimension to the emited telemetry data

[JanKrivanek]

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.

[JanProvaznik]

This seems blocked by VS OTel being enabled by default. Cardinality from Experiments does not seem meaningful.