SPINECORE-6443: add copy_target_arn_list which is a list of arns

[tom-gowland-nhs]

Description

• Change test condition to check against ArnNotEquals which is more precise than StringNotEquals (as discussed with @regularfry)
• Adds a new copy_target_arn_list variable which allows the list of restoration accounts to be passed in dynamically
• Adds a copy_targets local to retain the pre-existing default restoration account from the blueprint

Context

Required as we needed a way to pass through a different restoration account ARN as well as being able to specify multiple ARNS which are valid for restoration.

Type of changes

• Refactoring (non-breaking change)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would change existing functionality)
• Bug fix (non-breaking change which fixes an issue)

Checklist

• I am familiar with the contributing guidelines
• I have followed the code style of the project
• I have added tests to cover my changes
• I have updated the documentation accordingly
• This PR is a result of pair or mob programming

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