This properly propagates the go Context on down to all HTTP calls, which means that outgoing request have the OTLP trace context.
This also adds the Jaeger propagator to the list of OTEL propagators, so that Synapse properly gets the incoming trace context.
It also upgrades all the OTEL libraries
Jaeger spans can be sent as OTLP so this is mostly semantics for
the collector, which is more flexible if it accepts OTLP traces
rather than jaeger.thrift traces.
