Modify permission EC2::GetTransitGatewayPrefixListPreferences

[perzycharles]

What does this PR do?

Modify permission ec2:GetTransitGatewayPrefixListPreferences toec2:GetTransitGatewayPrefixListReferences

Motivation

A customer reported that the following error occurred after installing AWS integration with cloudformation.

Datadog is not authorized to perform action ec2:GetTransitGatewayPrefixListReferences

• AWS doesn't have a permission which is called GetTransitGatewayPrefixListPreferences https://docs.aws.amazon.com/service-authorization/latest/reference/list_amazonec2.html

• manual installation is using GetTransitGatewayPrefixListReferences https://docs.datadoghq.com/integrations/amazon_web_services/#aws-integration-iam-policy

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[perzycharles]

Hi @sabiurr thank you for having a look at this issue. Could you please merge this PR as well? It seems that I don't have permission to merge PR.