`NodeSDK` should accept multiple `metricReader`s

[trentm]

The NodeSDK (from @opentelemetry/sdk-node) constructor currently supports a metricReader option:

export interface NodeSDKConfiguration {
...
  /** @deprecated use logRecordProcessors instead*/
  logRecordProcessor: LogRecordProcessor;
  logRecordProcessors?: LogRecordProcessor[];
  metricReader: IMetricReader;
...
  /** @deprecated use spanProcessors instead*/
  spanProcessor?: SpanProcessor;
  spanProcessors?: SpanProcessor[];
...
}

AFAICT there isn't a way to specify multiple metric readers.

(Trying to get a handle on the registered MeterProvider after sdk.start() and adding additional MetricReaders isn't possible because (a) MeterProvider.addMetricReader() was dropped in SDK v2.0 and (b) one would likely run into #4112.)

Is there a reason to not add a metricReaders (plural) option to NodeSDKConfiguration and deprecate the singular metricReader -- as was done for spanProcessors and logRecordProcessors?

[pichlermarc]

no, there's no reason this was not done yet. IMO we should:

• introduce a metricReaders option
• deprecate the metricReader option

as you suggested.