Review and enhance tracing support for checkout service (Go)

[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.
• Services extend automatic instrumentation.
  • 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: Ensure sufficient breadth in trace features across services #42

Service: https://github.com/open-telemetry/opentelemetry-demo-webstore/blob/main/src/checkoutservice/README.md

[cartersocha]

Tracing is code complete