refactor: update enum types to remove duplicate member values (#19320)

CDK has some enums which use the same value for different enum members. This is done to support friendly names for EC2 instance and Subnet type. Having same value for differnt members causes the typescript compiler to ignore the members with same value and causes JSII not to generate the enum members in other languages. To fix this [JSII will throw an error](aws/jsii#3412) when enum members have the same value. Updating CDK code to ensure the build pass when this change lands in JSII

re #aws/jsii#3412


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