Support for a codec that can create Span Events from OpenTelemetry traces #6650

Is your feature request related to a problem? Please describe.
As a user of OpenTelemetry with traces, I would like to create pull-based pipeline that can pull the traces from sources like S3 or Kinesis Data Streams, and extract the spans and send them downstream to other processors and sinks.

Currently, the otel_traces and service_map rely on Span types, which does not work as is with the json codec.

Describe the solution you'd like
Either a new otel_traces codec, or an option under the existing json codec that will convert data into Spans from traces.

Additional context
Add any other context or screenshots about the feature request here.