Propagate TraceContext headers
Propagate TraceContext headers

Similar to T225711 & a92cccea, propagate the two W3C TraceContext
headers to any sub-requests made.

Propagating these two headers without modifying them or even parsing
them is allowed by the W3C TraceContext Recommendation:
https://www.w3.org/TR/trace-context/#design-overview

Bug: T320561

wikimedia/service-template-node,wikimedia/service-template-node