Add configuration for trace_id

[bnjjj]

By default we decided to disable the export of trace_id in response headers for several reasons.
The goal of this issue is to find what we need to configure the behavior of trace_id.

Here are 3 different features I detected:

• Expose or not the trace_id in response headers
• Specify the header name if we want to expose it and modify the default one (default: apollo-trace-id)
• Specify a custom propagator to indicate what's the header name to set the trace_id

Configuration example:

telemetry:
  tracing:
    experimental_expose_trace_id:
      enabled: true # default: false
      header_name: "my-trace-id" # default: "apollo-trace-id"
    propagation:
      custom_header: "x-request-id"
      jaeger: true

[BrynCooke]

Suggest that experimental_expose_trace_id is merged into the logging section in #2040

Maybe rename it to display_trace_id

header_name is maybe not be needed once propagation.custom_header is implemented as the trace id is available from the span.

[bnjjj]

I don't think the experimental_expose_trace_id should be in logging section, because it doesn't change the logging behavior, it will always display the trace_id in logs. It's all about the trace_id in response and request headers and then is still related only to trace. But if you think it might also be useful to have a way to not display the trace_id in logs, then I can also add a display_trace_id in logging section because this is related to logging.

And about header_name, as it's not inside propagation.custom_header but directly inside experimental_expose_trace_id it's not so obvious that the name is supposed to be a header name.