test: set feature flag for unique launch template names to fix integ tests

[marofke]

Problem

Integration tests were failing to deploy some stacks due to Launch template name collisions. This is due to the IMSDv2 aspect requiring a feature flag for a launch template name to be unique.

Solution

Set the feature flag in the cdk.json files for the integration tests

Testing

Synthesized a simple CDK app with and without the feature flag set, confirming a LaunchTemplate in the template receive a unique name with the feature flag.

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[jusiskin]

Looks good.

Only thing is the commit's category was fix: ... which should instead be test: .... I've renamed the PR so that should become the squashed commit (if the person merging reloads the page since I've renamed it).