Add references to metrics OTEPs (#4022)

specification/metrics/api.md

@@ -57,6 +57,7 @@ linkTitle: API
   * [Multiple-instrument callbacks](#multiple-instrument-callbacks)
 - [Compatibility requirements](#compatibility-requirements)
 - [Concurrency requirements](#concurrency-requirements)
+- [References](#references)
 
 <!-- tocstop -->
 
@@ -1327,3 +1328,19 @@ specific guarantees and safeties.
 
 **Instrument** - All methods of any Instrument are safe to be called
 concurrently.
+
+## References
+
+- [OTEP0003 Consolidate pre-aggregated and raw metrics APIs](https://github.com/open-telemetry/oteps/blob/main/text/metrics/0003-measure-metric-type.md)
+- [OTEP0008 Metrics observer specification](https://github.com/open-telemetry/oteps/blob/main/text/metrics/0008-metric-observer.md)
+- [OTEP0009 Metric Handle API specification](https://github.com/open-telemetry/oteps/blob/main/text/metrics/0009-metric-handles.md)
+- [OTEP0010 Rename "Cumulative" to "Counter" in the metrics API](https://github.com/open-telemetry/oteps/blob/main/text/metrics/0010-cumulative-to-counter.md)
+- [OTEP0049 Metric `LabelSet` specification](https://github.com/open-telemetry/oteps/blob/main/text/metrics/0049-metric-label-set.md)
+- [OTEP0070 Rename metric instrument Handles to "Bound Instruments"](https://github.com/open-telemetry/oteps/blob/main/text/metrics/0070-metric-bound-instrument.md)
+- [OTEP0072 Metric observer specification (refinement)](https://github.com/open-telemetry/oteps/blob/main/text/metrics/0072-metric-observer.md)
+- [OTEP0080 Remove the Metric API Gauge instrument](https://github.com/open-telemetry/oteps/blob/main/text/metrics/0080-remove-metric-gauge.md)
+- [OTEP0088 Metric Instruments](https://github.com/open-telemetry/oteps/blob/main/text/metrics/0088-metric-instrument-optional-refinements.md)
+- [OTEP0090 Remove the LabelSet object from the metrics API](https://github.com/open-telemetry/oteps/blob/main/text/metrics/0090-remove-labelset-from-metrics-api.md)
+- [OTEP0098 Explain the metric instruments](https://github.com/open-telemetry/oteps/blob/main/text/metrics/0098-metric-instruments-explained.md)
+- [OTEP0108 Metric instrument naming guidelines](https://github.com/open-telemetry/oteps/blob/main/text/metrics/0108-naming-guidelines.md)
+- [OTEP0146 Scenarios for Metrics API/SDK Prototyping](https://github.com/open-telemetry/oteps/blob/main/text/metrics/0146-metrics-prototype-scenarios.md)

specification/metrics/data-model.md

@@ -54,6 +54,7 @@ aliases: [/docs/reference/specification/metrics/datamodel]
   * [Sums: Delta-to-Cumulative](#sums-delta-to-cumulative)
     + [Sums: detecting alignment issues](#sums-detecting-alignment-issues)
     + [Sums: Missing Timestamps](#sums-missing-timestamps)
+- [References](#references)
 - [Footnotes](#footnotes)
 
 <!-- tocstop -->
@@ -1276,6 +1277,12 @@ For comparison, see the simple logic used in
 [statsd sums](https://github.com/statsd/statsd/blob/master/stats.js#L281)
 where all points are added, and lost points are ignored.
 
+## References
+
+- [OTEP0049 Metric `LabelSet` specification](https://github.com/open-telemetry/oteps/blob/main/text/metrics/0049-metric-label-set.md)
+- [OTEP0113 Integrate Exemplars with Metrics](https://github.com/open-telemetry/oteps/blob/main/text/metrics/0113-exemplars.md)
+- [OTEP0146 Scenarios for Metrics API/SDK Prototyping](https://github.com/open-telemetry/oteps/blob/main/text/metrics/0146-metrics-prototype-scenarios.md)
+
 ## Footnotes
 
 \[1\] OTLP supports data point kinds that do not satisfy these conditions; they are

specification/metrics/noop.md

@@ -33,6 +33,7 @@ linkTitle: No-Op
   * [Asynchronous UpDownCounter Observations](#asynchronous-updowncounter-observations)
   * [Asynchronous Gauge](#asynchronous-gauge)
   * [Asynchronous Gauge Observations](#asynchronous-gauge-observations)
+- [References](#references)
 
 <!-- tocstop -->
 
@@ -263,3 +264,7 @@ concurrently.
 
 The No-Op Asynchronous Gauge MUST NOT validate or retain any state about
 observations made for the instrument.
+
+## References
+
+- [OTEP0146 Scenarios for Metrics API/SDK Prototyping](https://github.com/open-telemetry/oteps/blob/main/text/metrics/0146-metrics-prototype-scenarios.md)

specification/metrics/sdk.md

@@ -84,6 +84,7 @@ linkTitle: SDK
 - [Numerical limits handling](#numerical-limits-handling)
 - [Compatibility requirements](#compatibility-requirements)
 - [Concurrency requirements](#concurrency-requirements)
+- [References](#references)
 
 <!-- tocstop -->
 
@@ -1775,3 +1776,9 @@ and `Shutdown` are safe to be called concurrently.
 
 **MetricExporter** - `ForceFlush` and `Shutdown` are safe to be called
 concurrently.
+
+## References
+
+- [OTEP0113 Integrate Exemplars with Metrics](https://github.com/open-telemetry/oteps/blob/main/text/metrics/0113-exemplars.md)
+- [OTEP0126 A Proposal For SDK Support for Configurable Batching and Aggregations (Basic Views)](https://github.com/open-telemetry/oteps/blob/main/text/metrics/0126-Configurable-Metric-Aggregations.md)
+- [OTEP0146 Scenarios for Metrics API/SDK Prototyping](https://github.com/open-telemetry/oteps/blob/main/text/metrics/0146-metrics-prototype-scenarios.md)

specification/metrics/sdk_exporters/otlp.md

@@ -60,3 +60,7 @@ The recognized (case-insensitive) values for `OTEL_EXPORTER_OTLP_METRICS_DEFAULT
   Use [Explicit Bucket Histogram Aggregation](../sdk.md#explicit-bucket-histogram-aggregation).
 * `base2_exponential_bucket_histogram`:
   Use [Base2 Exponential Bucket Histogram Aggregation](../sdk.md#base2-exponential-bucket-histogram-aggregation).
+
+## References
+
+- [OTEP0131 OTLP Exporters Configurable Export Behavior](https://github.com/open-telemetry/oteps/blob/main/text/metrics/0131-otlp-export-behavior.md)