Stdout to print temporality in user readable format (#1260)

Author: cijothomas

opentelemetry-stdout/CHANGELOG.md

@@ -4,6 +4,8 @@
 
 - Timestamp is additionally exported in user-friendly format.
   [#1192](https://github.com/open-telemetry/opentelemetry-rust/pull/1192).
+- MetricExporter - Temporality is exported in user-friendly format.
+  [#1260](https://github.com/open-telemetry/opentelemetry-rust/pull/1260).
 
 ## v0.1.0
 

opentelemetry-stdout/src/metrics/transform.rs

@@ -184,7 +184,11 @@ impl Serialize for Temporality {
     where
         S: Serializer,
     {
-        serializer.serialize_u8(*self as u32 as u8)
+        match &self {
+            Temporality::Cumulative => serializer.serialize_str("Cumulative"),
+            Temporality::Delta => serializer.serialize_str("Delta"),
+            Temporality::Unspecified => serializer.serialize_str("Unspecified"),
+        }
     }
 }