customize role name in log forwarder CFN template

[jpassaro]

What does this PR do?

Allow users to specify the prefix for the AWS/IAM role the Cloudformation stack creates

Motivation

In some regulated AWS environments, there are constraints on how resources can be named. That means the stack as it currently exists will fail because the auto-generated role name does not comply with these constraints. This change allows me to use the stack and comply with those constraints.

Testing Guidelines

Ran it in my organization's environment and observed that the role could be created.

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)
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