Add maintenance alert for Simple Forms

[Thrillberg]

Are you removing, renaming or moving a folder in this PR?

• [X] No, I'm not changing any folders (skip to TeamSites and delete the rest of this section)
• [ ] Yes, I'm removing, renaming or moving a folder

Did you change site-wide styles, platform utilities or other infrastructure?

• [X] No
• [ ] Yes, and I used the proxy-rewrite steps to test the injected header scenario

Summary

This PR adds a maintenance alert to Simple Forms.

Related issue(s)

https://github.com/orgs/department-of-veterans-affairs/projects/1443/views/3?sliceBy%5Bvalue%5D=Thrillberg&pane=issue&itemId=83348489&issue=department-of-veterans-affairs%7Cva.gov-team-sensitive%7C2017

Screenshots

Shortly before a maintenance window:

In a maintenance window:

What areas of the site does it impact?

Only Simple Forms