dd-trace-go: Improper parsing of W3C baggage headers may lead to DoS

Datadog tracing libraries that implement W3C baggage propagation parse incoming baggage HTTP headers without enforcing item-count or byte-size limits on the extract path. The DDTRACEBAGGAGEMAXITEMS default 64 and DDTRACEBAGGAGEMAXBYTES default 8192 limits were applied only to baggage injection, n...