add span attributes to frontend

[puckpuck]

Updates #49 to add new attributes to existing spans.

Changes

Adds attributes to frontend service spans
All handlers are wrapped with common attributes (session, request, currency, user).
Most handlers have application-specific attributes added
Defines an instr package that contains some semantic conventions

• Appropriate CHANGELOG.md updated for non-trivial changes
• Design discussion issue Ensure sufficient breadth in trace features across services #42 and Review and enhance tracing support for frontend (Go)  #49

This adds some conventions (ie: app. prefix) to attribute names. We should settle on clean conventions before pushing similar instrumentation to other services.

[cartersocha]

When I run your branch the spans look the same as the current version. Could you post a screenshot of your output?

[puckpuck]

This doesn't add spans, but rather span attributes to existing auto-instrumented spans.

[cartersocha]

Thanks for the pic. I was checking for attributes but had been glancing through the console output which doesn't have them for whatever reason.

LGTM

[cartersocha]

Are you planning on documenting this in the service readme?

[puckpuck]

Are you planning on documenting this in the service readme?

That's the next PR 😉