Fix the error of "Cannot export output ForwarderBucketName" or "Invalid policy" when deploying lambda forwarder using cloudformation template

[perzycharles]

What does this PR do?

When creating lambda forwarder with the following parameters, the stack would fail with errors Cannot export output ForwarderBucketName or Invalid policy .

• DdFetchLambdaTags: false
• DdFetchLogGroupTags: false
• DdForwarderBucketName: (empty)
• DdForwarderExistingBucketName: (empty)

Motivation

CLOUDS-4708
This issue could be replicated in my sandbox.

Testing Guidelines

Additional Notes

Types of changes

• Bug fix
• New feature
• Breaking change
• Misc (docs, refactoring, dependency upgrade, etc.)

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