PR for otelp-metrics

[bryce-b]

I'm opening this draft PR to get some feedback on the changes I've made to the existing api to support the otelp for metrics.

Here are key notes for these changes:

- Made MeterSdkProvider init mimic the TraceProvider init

        I decided to change the MetricSdkProvider.init method to take shared state objects as parameters,
        since this is how the TraceProvider operates. Alternatively, I could have move the default values
        into the MeterSharedState construction, but that would require making the NoopMetricProcessor &
        NoopMetricExporter public, which I'm not against, but seemed intentionally private.

- replaced MeterRegisteryKey with InstrumentationLibraryInfo

- Injected Resource into the MetricSdk stack
        I followed the same pattern as with the Trace Sdk.

[nachoBonafonte]

It looks great so far.
About making Noop... public, I cannot imagine a use case for a user of the library to use a NoopMetricProcessor or a NoopMetricExporter. I would only make public what can be useful for the user.

[bryce-b]

I cannot imagine a use case for a user of the library to use a NoopMetricProcessor or a NoopMetricExporter

I agree, the issue I ran into was using them as default values for the sharedMeterState's constructor, which would have required them to be public since they would be available in the constructor definition.

[bryce-b]

I'm looking for some guidance in the toProtoMetric method in Sources/Exporters/OpenTelemetryProtocol/metric/MetricsAdapter.swift

I'm not seeing a way to set min/max values. The closest proto metric I could find for the summary metrics was a histogram. I was thinking that the explicitBounds might satisfy the "min/max" issue, but I don't think that's quite right. Would exemplars be the means to capture the min max values?

[nachoBonafonte]

Not an expert here, but I would say so. Checking opentelemetry-go code, they have this method and in line 261 they convert to histogram with this. I hope it can help you

[nachoBonafonte]

Sorry for the delay in reviewing, i was OOO since last Wednesday.
The code looks really great, and I think that your changes made the usage much nicer and consistent. Just to be picky, I saw some styling issues mainly with multiple line breaks, but can be merged like this. (I use swiftformat for auto fixing style)

[nachoBonafonte]

Thanks a lot for your contribution.
Let me know if you cannot merge the PR and I will do.

[bryce-b]

I'll make sure I use swiftformat in the future! I'm not able to merge however; take it away!