fix c++ 20 STD::Allocator Warning

[jmklix]

Issue #, if available: https://github.com/aws/aws-sdk-cpp/issues/3001

Description of changes: replace old and deprecated std::allocator. https://github.com/awslabs/aws-crt-cpp/pull/191/files Similar PR in aws-crt-cpp: https://github.com/awslabs/aws-crt-cpp/pull/191

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