Support WithAttributes for default MeterProvider

[austince]

Problem Statement

For adding a static set of attributes to spans, the SpanConfig offers a nice way (along with the WithAttributes option builder) to accomplish this.

opentelemetry-go/trace/config.go

Lines 218 to 229 in 7aba25d

	// WithAttributes adds the attributes related to a span life-cycle event.
	// These attributes are used to describe the work a Span represents when this
	// option is provided to a Span's start or end events. Otherwise, these
	// attributes provide additional information about the event being recorded
	// (e.g. error, state change, processing progress, system event).
	//
	// If multiple of these options are passed the attributes of each successive
	// option will extend the attributes instead of overwriting. There is no
	// guarantee of uniqueness in the resulting attributes.
	func WithAttributes(attributes ...attribute.KeyValue) SpanStartEventOption {
	return attributeOption(attributes)
	}

There doesn't seem to be compatible functionality for the Metrics API. The motivation is the same as for spans, where some meters could be given additional information about what is being metered.
Let's say we have two k8s services that our process talks to via http.Clients. We want to track the number of requests and have the ability to group by service name. The conventional attributes are too low-level to be able to do this nicely.

Proposed Solution

Similar to the WithAttributes(..) func for spans, we could add a new MeterOption that accepts a slice of attributes to attach.

Alternatives

Use the Resource in the MeterProvider. This seems to be a good place for global attributes but not for dynamic local ones.

Prior Art

I can't find any similar examples in the Java or .NET implementations.

Additional Context

Discussed a bit on Slack: https://cloud-native.slack.com/archives/C01NPAXACKT/p1669499929785919

[Aneurysm9]

This functionality would need to be defined in the OpenTelemetry Specification before we could begin any implementation here.

[austince]

It looks like this was actually already added to the spec in 1.13.0: https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/metrics/api.md#get-a-meter

[since 1.13.0] attributes (optional): Specifies the instrumentation scope attributes to associate with emitted telemetry.

Part of the "Scope Attributes" effort: https://github.com/open-telemetry/oteps/blob/main/text/0201-scope-attributes.md#meter

Do you read this the same way? If so, I can update this issue to reflect the ask better. I'd also be happy to work on a PR.

[austince]

Or is this a duplicate of #3368? EDIT: I think so, I'll close this and track that.

[Aneurysm9]

Instrumentation scope attributes may be the thing you're looking for, but there are still unresolved questions in the spec SIG regarding whether they are identifying for instruments produced by a meter bearing them or not.

[austince]

Hmm, alright. I've seen those comments elsewhere. Thanks for the pointers, I'll keep up with those discussions 👍🏼