bug: Use requsted deploymentTarget for StackSets

[mbevc1]

Describe the bug
When using a OUs as a depletion target in customisations config it gets translated to accounts before synthesised to CFN.

To Reproduce

Provide this to an empty OU:

        organizationalUnits:
          - Some_OU

It fails to apply due an empty account list.

Expected behavior
We should be able to still apply customisations to an empty OU.

Please complete the following information about the solution:

• Version: [e.g. v1.10.1]

To get the version of the solution, you can look at the description of the created AWS CloudFormation stack used to install the LZA (AWSAccelerator-InstallerStack). For example, "(SO0199) Landing Zone Accelerator on AWS. Version 1.5.1.". If the description does not contain the version information, you can look at the Parameters of the stack for the RepositoryBranchName as that should contain the version number.

• Region: [e.g. eu-west-1]
• Was the solution modified from the version published on this repository?
• If the answer to the previous question was yes, are the changes available on GitHub?
• Have you checked your service quotas for the services this solution uses?
• Were there any errors in the CloudWatch Logs? no

Screenshots
n/a

Additional context
n/a