Injecting credentials into C++ S3 CRT SDK

It turns out that there is a constructor for the S3CrtClient that accepts a credentials argument. Looks like that is the way to go.

S3CrtClient(const Aws::Auth::AWSCredentials& credentials, const Aws::S3Crt::ClientConfiguration& clientConfiguration = Aws::S3Crt::ClientConfiguration(), Aws::Client::AWSAuthV4Signer::PayloadSigningPolicy signPayloads = Aws::Client::AWSAuthV4Signer::PayloadSigningPolicy::Never, bool useVirtualAddressing = true, Aws::S3Crt::US_EAST_1_REGIONAL_ENDPOINT_OPTION USEast1RegionalEndPointOption = Aws::S3Crt::US_EAST_1_REGIONAL_ENDPOINT_OPTION::NOT_SET);