Pre-release: Update version to 0.12.0 (aws-observability#462)

This PR updates the version to 0.12.0.

By submitting this pull request, I confirm that you can use, modify,
copy, and redistribute this contribution, under the terms of your
choice.

Author: ezhang6811

aws-opentelemetry-distro/src/amazon/opentelemetry/distro/version.py

@@ -1,4 +1,4 @@
 # Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
 # SPDX-License-Identifier: Apache-2.0
 
-__version__ = "0.11.0.dev0"
+__version__ = "0.12.0"