Adds aws tip to cicd add variable modal

What does this MR do?

Adds an alert (tip) for AWS guidance when adding an AWS variable.

issue: #207830 (closed)

Screenshots

mobile:

screenshot:

screencast:

Screen_Recording_2020-06-09_at_10.00.06_AM

• Code review guidelines
• Style guides
• Separation of EE specific content

Availability and Testing

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