Migration plan for using SpanKind from the old way of including "Sent"/"Recv" in span name

[voidzcy]

This was asked in https://github.com/census-instrumentation/opencensus-java/issues/1054#issuecomment-603977913, but got not reply. Raise an issue here.

gRPC is trying to migrate to use SpanKind (see https://github.com/grpc/grpc-java/pull/6732), but since Span name is changed, this seems to be a "flip the switch" change for traffic monitoring pipelines. How should we migrate this in gRPC for OSS without breaking open-source users' traffic monitoring pipelines?