Updates AWS EKS service role name help text to clarify it is distinct from provision role

What does this MR do?

Changes service role help text to inform user that the role name is distinct from the role used to authenticate with AWS.

Screenshots

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

Not needed

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers