docs: add instruments to left-nav (#4968)

Add instruments page to left-nav, and update related pages.

docs/source/config.json

@@ -128,6 +128,7 @@
         "Zipkin": "/configuration/telemetry/exporters/tracing/zipkin"
       },
       "Instrumentation": {
+        "Instruments" : "/configuration/telemetry/instrumentation/instruments",
         "Spans" : "/configuration/telemetry/instrumentation/spans",
         "Selectors" : "/configuration/telemetry/instrumentation/selectors",
         "Standard attributes": "/configuration/telemetry/instrumentation/standard-attributes",

docs/source/configuration/telemetry/exporters/metrics/overview.mdx

@@ -1,5 +1,5 @@
 ---
-title: Router Metrics
+title: Metrics exporters
 subtitle: Export Apollo Router metrics
 description: Collect and export metrics from the Apollo Router for Prometheus, OpenTelemetry Protocol (OTLP), Datadog, and New Relic
 ---

docs/source/configuration/telemetry/instrumentation/instruments.mdx

@@ -8,25 +8,20 @@ import RouterServices from '../../../../shared/router-lifecycle-services.mdx';
 
 <PremiumFeature linkWithAnchor="https://www.apollographql.com/pricing#observability"/>
 
-An **instrument** is used to collect data and report measurements to a metric backend. The Apollo Router supports the following metric instruments: 
+An _instrument_ in the router collects data and reports measurements to a metric backend. Supported instruments include standard instruments from OpenTelemetry, standard instruments for the router's request lifecycle, and custom instruments. Supported instrument kinds are counters and histograms.
 
-* Counter
-* Histogram 
+You can configure instruments in `router.yaml` with `telemetry.instrumentation.instruments`.
 
-Instruments in the router are configurable in `router.yaml` as `telemetry.instruments`.
+### OpenTelemetry standard instruments
 
-### Standard instruments
-
-OpenTelemetry semantic conventions define several standard metric instruments that are available and configurable in the router:
+OpenTelemetry specifies multiple [standard metric instruments](https://opentelemetry.io/docs/specs/semconv/http/http-metrics/) that are available in the router:
 
 * `http.server.active_requests` - The number of active requests in flight.
 * `http.server.request.body.size` - A histogram of request body sizes for requests handled by the router.
 * `http.server.request.duration` - A histogram of request durations for requests handled by the router.
 * `http.server.response.body.size` - A histogram of response body sizes for requests handled by the router.
 
-For more information, see the [OpenTelemetry semantic conventions for HTTP metrics](https://opentelemetry.io/docs/specs/semconv/http/http-metrics/).
-
-These standard instruments are configurable in `router.yaml`:
+These instruments are configurable in `router.yaml`:
 
 ```yaml title="router.yaml"
 telemetry:
@@ -39,7 +34,7 @@ telemetry:
         http.server.response.body.size: true # (default false)
 ```
 
-Standard instruments can be customized by attaching or removing attributes.
+They can be customized by attaching or removing attributes. See [attributes](#attributes) to learn more about configuring attributes.
 
 ```yaml title="router.yaml"
 telemetry:
@@ -52,17 +47,19 @@ telemetry:
             http.request.method: true
 ```
 
-See the [attributes](#attributes) configuration for more information.
+### Apollo standard instruments
+
+To learn about standard metric instruments for the router's request lifecycle, see [Apollo Router instruments](./standard-instruments).
 
 ### Custom instruments 
 
 <PremiumFeature linkWithAnchor="https://www.apollographql.com/pricing#observability"/>
 
-You can define custom instruments on the router, supergraph and subgraph services in the router pipeline.
+You can define custom instruments on the router, supergraph, and subgraph services in the router pipeline.
 
 <Note>
 
-When defining a custom instrument, make sure to reference the [OpenTelemetry semantic conventions](https://opentelemetry.io/docs/specs/semconv/general/metrics/).
+When defining a custom instrument, make sure to reference [OpenTelemetry semantic conventions](https://opentelemetry.io/docs/specs/semconv/general/metrics/).
 
 </Note>
 

docs/source/configuration/telemetry/instrumentation/standard-instruments.mdx

@@ -6,7 +6,7 @@ description: Reference of standard metric instruments for the Apollo Router's re
 
 ## Standard metric instruments
 
-The Apollo Router provides a set of non-configurable metric instruments that expose detailed information about the Router's request lifecycle.
+The Apollo Router provides a set of non-configurable metric instruments that expose detailed information about the router's request lifecycle.
 
 These instruments can be consumed by configuring a [metrics exporter](../exporters/metrics/overview).
 

docs/source/configuration/telemetry/overview.mdx

@@ -94,15 +94,17 @@ Logs can be consumed by [logging exporters](./exporters/logging/overview) and as
 
 ### Metrics and instruments
 
-Metrics monitor aggregate information about the Apollo Router. Metrics include histograms, gauges, and counts. An individual metric is called an **instrument**. Examples of instruments include:
+Metrics are measurements of the router's behavior that can be exported and monitored. Different kinds of metrics include histograms, gauges, and counts. 
+
+Metrics can be consumed by _exporters_. See [Metrics exporters](./exporters/metrics/overview) for an overview of supported exporters.
+
+An individual metric is called an _instrument_. Example instruments of the router include:
 
 * Number of received requests 
 * Histogram of request durations
 * Number of in-flight requests
 
-You can find a full list of instruments in the [instrument documentation](./instrumentation/standard-instruments).
-
-Metrics can be consumed via [metrics exporters](./exporters/metrics/overview).
+See [Instruments](./instrumentation/instruments) for an overview of available instruments and a guide for configuring and customizing instruments.
 
 ### Traces and spans