SDKv3-06: Update cdk-assets

[TheRealAmazonKendra]

Context

The AWS SDK V2 is being deprecated. We need to remove all uses of it from the CDK.

Task Description

Update cdk-assets to use sdkv3 and update the locations in aws-cdk required so that the types used are the same.

Known uses:

• lib/aws.ts: this generates a default client that is used extensively elsewhere in this package and in aws-cdk
• lib/private/handlers/container-image.ts: creates an ECR client that is used in a few locations
• test/mock-aws.ts

Acceptance Criteria

1. sdkv2 is completely removed from the cdk-assets package
2. Updates are made where needed in aws-cdk to not cause type confilcts
3. All tests (unit and integ) pass after the change has been made.