Currently Mistal doesn`t support distribution tracing, which means
that there`s no way to propagate traceId/spanId from an execution to
related actions/notifications.
It leads us to an issue, because according to distribution tracing
principles "traceId" should remain the same during the discovery
process, which includes Mistral worflow execution.
Proposed solution is to keep some headers from execution request
and propagate them later to actions/notifications.
Regexp can be stored as env variable to define headers which
will be propagated.
Implements blueprint add-headers-propagation
Change-Id: Id8cc900a7d94286e79f1ece4dc4177383263f55c
737e09646f