fix(migrate-template-gen): update gen1 stack with empty tags to suppo…

[abhi7cr]

Description of changes

Add empty stack level tags for gen1 stack preprocessing update to support stack refactoring later. This is a known issue with refactor that is being worked in and is a temporary solution.

Description of how you validated changes

local testing

Checklist

• [x] PR description included
• [x] yarn test passes
• [x] Tests are changed or added
• [ ] Relevant documentation is changed or added (and PR referenced)
• [ ] New AWS SDK calls or CloudFormation actions have been added to relevant test and service IAM policies
• [ ] Pull request labels are added

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