[SCENARIO] Dropped Attributes

Add a scenario to demonstrate a trace containing spans that has some dropped attributes. Demonstrated by a non-zero value in the `droppedAttributesCount` field.

I've also raised (https://github.com/open-telemetry/opentelemetry-proto/issues/745) that the documentation about when / why things are "dropped" is either incomplete or hard to find so it's hard for end users to understand why an event might be dropped.

## Example JSON

```
{
"traceId": trace_id,
"spanId": secrets.token_hex(8),
"name": "span",
"kind": "SPAN_KIND_UNSPECIFIED",
"start_time_unix_nano": span_start_time,
"end_time_unix_nano": span_end_time,
"droppedAttributesCount": 27,
"attributes": [],
"events": [],
"droppedEventsCount": 0,
"status": {
"code": get_span_status_int("OK")
}
}
```