Prevent creating ForwarderBucket if it will not be used

[jpassaro]

What does this PR do?

Teach the Cloudformation template to avoid creating the "ForwarderBucket" resource if it won't be used.

Motivation

My organization has strict controls on the creation of S3 buckets; I can't use this template unless there is a way to avoid creating one.

Testing Guidelines

Ran it in my organization's AWS account and observed no errors.

Additional Notes

Types of changes

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

Check all that apply

• This PR's description is comprehensive
• This PR contains breaking changes that are documented in the description
• This PR introduces new APIs or parameters that are documented and unlikely to change in the foreseeable future
• This PR impacts documentation, and it has been updated (or a ticket has been logged)
• This PR's changes are covered by the automated tests
• This PR collects user input/sensitive content into Datadog
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• This PR passes the unit tests
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