[en] add gauge assync definition (#5698)

Author: maryliag

content/en/docs/concepts/signals/metrics.md

@@ -69,6 +69,9 @@ The instrument kind is one of the following:
   size).
 - **Gauge**: Measures a current value at the time it is read. An example would
   be the fuel gauge in a vehicle. Gauges are asynchronous.
+- **Asynchronous Gauge**: Same as the **Gauge**, but is collected once for each
+  export. Could be used if you don't have access to the continuous changes, but
+  only to the aggregated value.
 - **Histogram**: A client-side aggregation of values, such as request latencies.
   A histogram is a good choice if you are interested in value statistics. For
   example: How many requests take fewer than 1s?

content/en/docs/languages/go/instrumentation.md

@@ -302,7 +302,7 @@ OpenTelemetry Go currently supports the following instruments:
 - Histogram, a synchronous instrument that supports arbitrary values that are
   statistically meaningful, such as histograms, summaries, or percentile
 - Synchronous Gauge, a synchronous instrument that supports non-additive values,
-  such as room temperature.
+  such as room temperature
 - Asynchronous Gauge, an asynchronous instrument that supports non-additive
   values, such as room temperature
 - UpDownCounter, a synchronous instrument that supports increments and