SpanProcessor without sampling

[jeffreye]

What are you trying to achieve?
Sending traces with different strategies

What did you expect to see?
toggle sampled value for processors
configurable via envs/properties
I think we can take advatange of SamplingDecision.RECORD_ONLY which seems to be perfect use case for this and unused in the current specification.

Additional context.
We would like to have two different span exporters:
gRPC -> sending to a trace store ( need sampling to reduce storage requirement)
customized exporter -> sending to ETL ( doesn't need sampling, but it may take a while to be used by devs)

Add any other context about the problem here. If you followed an existing documentation, please share the link to it.