S3A AssumedRole credentials provider should use Instance Role credentials in chain for assuming role

The AssumedRoleCredentialsProvider today creates its own credential provider set to use when getting session credentials from STS. This includes only environment variables and simple credentials provider. https://github.com/apache/hadoop/blob/952d707240cb7dd088820d8b39e705b77fa3b6c4/hadoop-tools/hadoop-aws/src/main/java/org/apache/hadoop/fs/s3a/auth/AssumedRoleCredentialProvider.java#L114-L116

It should at least include EC2 Instance Role credentials, possibly others, by default.