fix: Correct IRSA module name used to not default to null through coalesce()

[bryantbiggs]

What does this PR do?

• Correct IRSA module name used to not default to null through coalesce()
  • Because of the use of optional variable attributes, when a value is not provided it defaults to null which is a valid value inside a try() block and for IAM role names. When the value is null, Terraform will provide a value for it which is not the desired default behavior. Instead, we want to use a custom name if provided, otherwise fall back to the format provided by the module

Motivation

• Closes [Bug]: irsa roles are not being created with correct name for aws_for_fluentbit #788

More

• Yes, I have tested the PR using my local account setup (Provide any test evidence report under Additional Notes)
• Yes, I have added a new example under examples to support my PR
• Yes, I have created another PR for add-ons under add-ons repo (if applicable)
• Yes, I have updated the docs for this feature
• Yes, I ran pre-commit run -a with this PR

Note: Not all the PRs required examples and docs except a new pattern or add-on added.

For Moderators

• E2E Test successfully complete before merge?

Additional Notes