Review and enhance metric support for ad service service (Java)

[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

[jlawrienyt]

Proposed Solution:

The Ad Service already has some business logic around whether to deliver targeted ads or random ads, based on the context and ad availability. We should capture this decision as a single metric named app.ads.ad_requests with two dimensions: ad_request_type with possible values TARGETED and NOT_TARGETED; and ad_response_type with possible values TARGETED and RANDOM.

Currently, the code path that would serve a random ad is not being exercised by the load generator, nor is it possible to exercise it by browsing the demo site, because all products have categories with associated ads. I propose we add a new product in a new category that does not have an associated ad in order to demonstrate this behavior. We should probably do this regardless of the metrics change as the getRandomAds span is not currently getting produced.

cc @puckpuck

[austinlparker]

Closing as basic metrics have been added