Resource is missing in MetricRecord for MetricExporter

[legendecas]

Is your feature request related to a problem? Please describe.
MetricExporter can not get access to Metric's resource in the current API.

Describe the solution you'd like
Add a parameter for resources like go's implementation https://github.com/open-telemetry/opentelemetry-go/blob/master/exporters/metric/prometheus/prometheus.go#L171

MetricExporter.export(
  resource: Resource,
  metrics: MetricRecord[],
  resultCallback: (result: ExportResult) => void
): void;

However, altering the order of the parameters will be a breaking change.

[dyladan]

I am fine with this sort of breaking change as it is entirely contained within the SDK. We need to pass resource so I don't see a strong reason not to adopt this, we will just need to bump the minor version.

[dyladan]

It looks like there is an open spec issue for this open-telemetry/opentelemetry-specification#508

[mwear]

I think the spec issue and the proposal above both make sense. We should discuss those further at the Spec SIG. For now, we should go with what is specified in the SDK Resource spec

It says:

Analogous to distributed tracing, when used with metrics, a resource can be associated with a MeterProvider. When associated with a MeterProvider, all Metrics produced by any Meter from the provider will be associated with this Resource.

Metric instances have a reference to a Resource. It just needs to be exposed on MetricRecord. See: https://github.com/open-telemetry/opentelemetry-js/blob/master/packages/opentelemetry-metrics/src/Metric.ts#L45.

You can assign this to me @dyladan.