Use different HTTP header for distributed trace context

#### Is your question related to a specific version? If so, please specify:
Azure Function (in-process), .NET 6

#### What language does your question apply to? (e.g. C#, JavaScript, Java, All)
C#

#### Question
Instead of the default `traceparent` HTTP header I want to use another value, e.g. `X-Correlation-Id`.

I tried using a custom `DistributedContextPropagator` (and setting it in the Startup `DistributedContextPropagator.Current = new MyCusomtPropagator();`), but it seems to be unused. At least its not executed when I trigger the HTTP function.

How should this be configured?

Start at the Azure Function in-process Startup configuration and the HTTP-trigger entry path, then trace where traceparent is read and whether DistributedContextPropagator.Current is consulted. Confirm the supported configuration path for a custom header such as X-Correlation-Id, and document a reproducible result for .NET 6.

Written by the indexing model from the issue text.