Set OTLP grpc as the default metrics exporter for auto-instrumentation (#1127)

Author: aabmass

Diff for: CHANGELOG.md

@@ -23,6 +23,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   ([#1082](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/1082))
 - Added `opentelemetry-instrumention-confluent-kafka`
   ([#1111](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/1111))
+- Set otlp-proto-grpc as the default metrics exporter for auto-instrumentation
+  ([#1127](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/1127))
 
 
 ## [1.12.0rc1-0.31b0](https://github.com/open-telemetry/opentelemetry-python/releases/tag/v1.12.0rc1-0.31b0) - 2022-05-17

Diff for: opentelemetry-distro/src/opentelemetry/distro/__init__.py

@@ -14,7 +14,10 @@
 
 import os
 
-from opentelemetry.environment_variables import OTEL_TRACES_EXPORTER
+from opentelemetry.environment_variables import (
+    OTEL_METRICS_EXPORTER,
+    OTEL_TRACES_EXPORTER,
+)
 from opentelemetry.instrumentation.distro import BaseDistro
 from opentelemetry.sdk._configuration import _OTelSDKConfigurator
 
@@ -32,3 +35,4 @@ class OpenTelemetryDistro(BaseDistro):
     # pylint: disable=no-self-use
     def _configure(self, **kwargs):
         os.environ.setdefault(OTEL_TRACES_EXPORTER, "otlp_proto_grpc")
+        os.environ.setdefault(OTEL_METRICS_EXPORTER, "otlp_proto_grpc")