fix: removes preparepp() cdkV1 shim layer

[akshbhu]

Description of changes

For Context :

We removed the prepareApp implementation exported in cdk V1 and replaced with ShimImplementation : https://github.com/aws-amplify/amplify-cli/blob/cdkv2/packages/amplify-category-geo/src/service-utils/prepare-app.ts required to generate same cfn.

The fix is inspired by https://github.com/aws/aws-cdk/blob/bd056d1d38a2d3f43efe4f857c4d38b30fb9b681/packages/%40aws-cdk/assertions/lib/template.ts#L298-L310 .
This performs deep evaluation of the stack and fills missing dependsOn Custom lambda resources.

There are two changes in PR

1. Synthesizing cfn template using root.synth() which generates full cloud assembly with dependencies. Similar behaviour is not achieved by _.toCloudformation() w/o prepareApp().
2. Calling root.synth() in cdkV2 uses defaultStackSynthesizer by default which was creating default cfn parameters for bootstartping cdk project. This is changed to previous behaviour of using lagacyStacksyntheiser

Description of how you validated changes

• unit tests passing and e2e test passed with previous snapshot
• cloud-e2e workflow: https://app.circleci.com/pipelines/github/aws-amplify/amplify-cli/12229/workflows/e600fa15-a6dc-4a75-a9c9-019b9be9a5b1

Checklist

• PR description included
• yarn test passes
• 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

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[jhockett]

nit: I'd prefer this broken up for readability

Suggested change

	return JSON.parse(fs.readFileSync(path.join(assembly.directory, this.templateFile)).toString('utf-8'));
	const template = fs.readFileSync(path.join(assembly.directory, this.templateFile);
	return JSON.parse(template).toString('utf-8'));