STSAssumeRoleSessionCredentialsProvider is deprecated

[Jtcollins]

The standard convention of using cross-account credentials seems to be to set AWSCredentialsProvider to AWSCredentialsProvider = STSAssumeRoleSessionCredentialsProvider|<stream_arn>|<session_name> in the samples.properties config file.

However, STSAssumeRoleSessionCredentialsProvider seems to be deprecated and the new STSAssumeRoleSessionCredentialsProvider.Builder doesn't seem to work due to the fact it needs to build after-the-fact. This may require changes in the underlying multilang daemon.

There is also a related PR to add assume role support, however it doesn't address the deprecated functionality issue: #70