Maintenance Mode: Form UX Improvements

What does this MR do and why?

Fixes Maintenance Mode: Form UX Bugs (#556584 - closed)

When updating Maintenance Mode there are some backend restrictions that are not reflected in UI that can cause some frustrating albeit minor work/time loss.

Backend Restrictions:

1. Banner message cannot exceed 255 characters
2. Banner messages are not saved if the user doesn't also enable maintenance mode
3. Banner messages previously saved are erased if user disables maintenance mode

This MR is focused on better communicating all 3 of the above restrictions in the UI as well as generally a more intuitive experience in when managing this setting.

Screenshots or screen recordings

Before

Restriction 1	Restriction 2	Restriction 3
Restriction 1	Restriction 2	Restriction 3

After - Demo of new experience

Screen_Recording_2025-07-29_at_12.17.37_PM

How to set up and validate locally

1. Go to Admin > Settings > General
2. Scroll down to the Maintenance Mode settings and expand it
3. Ensure you can enable/disable maintenance mode
4. When enabled a Banner Message text box should appear
5. If you enter over 255 characters in the text box ensure you cannot save and the UI says X characters over limit.
6. Ensure if you disable maintenance mode with a banner message in the box a pop up modal warns you the message will be lost.