Review and enhance metric support for recommendation service (Python)

[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

[mviitane]

I can check this one.