Review and enhance tracing support for cart service (C#)

[cartersocha]

The following is a list of requirements that we need to evaluate before declaring v1 for trace telemetry. These requirements are across the entire application; Not all services will meet all requirements. Determine the relevant features for this service.

• [ ] Automatic Instrumentation is being used where appropriate.
• [ ] Library instrumentation is being used if automatic instrumentation is unavailable.
• [x] Services extend automatic instrumentation.
  • [x] New attributes/events attached to existing spans.
  • [ ] New spans are being created from existing spans.
• [ ] Automatic and Manual Context Propagation are being demonstrated.
• [ ] Telemetry is not being sampled upfront.
• [ ] Telemetry is not being filtered upfront.
• [ ] Baggage is being set and read appropriately (i.e., baggage must be explicitly set as attributes on spans)
• [ ] Update the centralized tracing doc

Referencing: https://github.com/open-telemetry/opentelemetry-demo-webstore/issues/42

Service: https://github.com/open-telemetry/opentelemetry-demo-webstore/tree/main/src/cartservice