Access to underlying libhoney::Client

[Procrat]

Hi there! Thank you for maintaining the tracing-honeycomb crate!

We would like to add an extra default field to the Honeycomb client. However, I don't think we're currently able to do so. Would you be open to making some crate-public fields public?

This snippet

let mut client = libhoney::init(honeycomb_config);
client.add_field("my-field", some_value);
// let telemetry = HoneycombTelemetry::new(Mutex::new(client), Some(sample_rate));
let telemetry = HoneycombTelemetry {
    reporter: LibhoneyReporter::new(client),
    sample_rate: Some(sample_rate),
};
let layer = TelemetryLayer::new("my-service", telemetry, move |tracing_id| SpanId { tracing_id })

currently fails with

error[E0451]: field `reporter` of struct `tracing_honeycomb::HoneycombTelemetry` is private
   |
73 |             reporter: LibhoneyReporter::new(client),
   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ private field

error[E0451]: field `sample_rate` of struct `tracing_honeycomb::HoneycombTelemetry` is private
   |
74 |             sample_rate: Some(sample_rate),
   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ private field

error[E0451]: field `tracing_id` of struct `tracing_honeycomb::SpanId` is private
  --> narrative-maxwell/src/util/tracing.rs:76:78
   |
76 |         TelemetryLayer::new("maxwell", telemetry, move |tracing_id| SpanId { tracing_id })
   |                                                                              ^^^^^^^^^^ private field