Review and enhance metric support for check out service (Go)

[cartersocha]

The following are requirements for metrics in the project. Not all services will meet all requirements.

• Service metrics should not be duplicative of trace-derived metrics.
• Services should emit multiple business metrics where appropriate.
• Services should emit trace exemplars for their metrics.
• Services should use push metrics where possible.
• Services should explicitly read baggage where needed.
• Collectors should perform metric transforms to normalize resource and service metrics.

Referencing issue: #43

[austinlparker]

Closing as basic metric support has been added