MdcPropagatingDispatcherConfigurator

This provides an ExecutionContext which copies MDC data over in prepare(). Since prepare() is implicitly called by Promise#onComplete, MDC data will not be lost on many async boundaries. It may still be required to explicitly call prepare() in some scenarios (e.g. with pekko)

This can be enabled with.

 pekko.actor.default-dispatcher {
   type = "uk.gov.hmrc.play.bootstrap.dispatchers.MdcPropagatingDispatcherConfigurator"
 }