Add scope attributes

[jack-berg]

Scopes have attributes. We need to extend our data model to support this, which is particularly important metrics and for the event api where a scope attribute called event.domain seems likely to be required.

There are a number of small things to do for scope attributes to be supported:

• [x] Extend InstrumentationScopeInfo with attributes #4696
• [ ] Extend TracerBuilder to optionally specify attributes #4711
• [ ] Extend MeterBuilder to optionally specify attributes #4711
• [ ] Extend LogEmitterBuilder to optionally specify attributes #4711
• [x] Serialize scope attributes in OTLP #4712
• [ ] Serialize scope attributes in zipkin
• [ ] Serialize scope attributes in jaeger

[jack-berg]

Serialization of jaeger and zipkin scope attributes is blocked on spec issue #2744.