internal/tracer/otel: add and use Jaeger propagator

Created by: bobheadxi

Closes #38232 (closed) - turns out there's an Jaeger propagator we're supposed to use for the opentelemetry library. After enabling it and using the composite propagator on both ends of the tracer, we now have linked traces to Zoekt's opentelemetry Jaeger implementation again in Jaeger with opentelemetry enabled:

Test plan

sg start, &trace=1