Document that (*Collector).Run shouldn't be called after shutdown (#3604)
Document that (*Collector).Run shouldn't be called after shutdown (#3604)

Currently, the behavior allows collector to be shutdown and restarted by Run. But we shouldn't promise this behavior given it may complicate the Collector implementation over time even though it doesn't present a significant advantage to the alternative: reconstructing a collector and running it.
open-telemetry/opentelemetry-collector-contrib,open-telemetry/opentelemetry-collector,open-telemetry/opentelemetry-collector,open-telemetry/opentelemetry-collector,open-telemetry/opentelemetry-collector-contrib