APM Server version (apm-server version): 9.2

Description of the problem including expected versus actual behavior:

kibana is showing some otel span from self-instrumentation as "unknown".

Ensure all spans have a SpanKind associated with it

Steps to reproduce:

1. enable self-instrumentation
2. check kibana traces
3. see a mix of "request" and "unknown kind"

Provide logs (if relevant):