Bootstrap container repository can be deleted in linked accounts

[dbaileyut]

Describe the bug
Folks with sufficient privileges in workload accounts can delete the "cdk-accel-container-assets-[AccountNumber]-[region]" ECR repository resulting in a failed upgrade in the Bootstrap action of the Booststrap stage and the error:

AWSAccelerator-CDKToolkit | 0/14 | 10:37:08 PM | UPDATE_FAILED | AWS::ECR::Repository | ContainerAssetsRepository Resource handler returned message: "The repository with name 'cdk-accel-container-assets-[WorkloadAccountNumber]-us-east-1' does not exist in the registry with id '[WorkloadAccountNumber]' (Service: Ecr, Status Code: 400, Request ID: [GUID])" (RequestToken: [GUID], HandlerErrorCode: NotFound)

To Reproduce
In a workload account, delete the "cdk-accel-container-assets-[AccountNumber]-[region]" repository and attempt an LZA upgrade.

Expected behavior
A policy should prevent the repository from being deleted except from the management account.

Please complete the following information about the solution:

• Version: v1.11.0 (upgrading from v1.9.1)
• Region: us-east-1
• Was the solution modified from the version published on this repository? No
• If the answer to the previous question was yes, are the changes available on GitHub? N/A
• Have you checked your service quotas for the services this solution uses? Yes
• Were there any errors in the CloudWatch Logs? No

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Additional context
Add any other context about the problem here.

[Athanasii]

Thank you for the report. We are looking into it.