normalize PyPI configuration in all Python repositories

[mattsb42-aws]

Following on from aws/aws-encryption-sdk-python#297 the configuration in all our Python repos should be updated to be consistent.

• https://github.com/aws/aws-encryption-sdk-python/
  • chore: centralize twine configuration logic and remove dependency on pypirc aws-encryption-sdk-python#297
• https://github.com/aws/aws-encryption-sdk-cli/
• https://github.com/aws/aws-dynamodb-encryption-python/
• https://github.com/aws/base64io-python/
• https://github.com/awslabs/secrets-helper/