Info about restart mandatory for config of maintenance page missing

[Anouchka-M]

On the custom error page we add some info that we don't add in the maintenance page
https://doc.scalingo.com/platform/app/custom-error-page#custom-error-pages

In order to prevent the page to be fetched at each request, the content is cached in the router’s memory. Hence we limit the size of this page to 10MB.

It is mandatory to restart the application for the configuration of these pages to be taken into account.

Related to this conversation : https://app.intercom.com/a/inbox/w4oogu7s/inbox/admin/5676128/conversation/12375700338478?view=List

The use case is that during maintenance, the end of maintenance time changed. So the user needed to update their message. In order to do so, they had to scale quickly back at 1 so the configuration is taken into account, and then scale back to 0.