Create site-wide banner for manage.get.gov

[vickyszuchin]

Issue description

If the registrar functionality is unavailable, we should inform users on manage.get.gov. A banner to communicate the situation will be helpful. Currently, we do not have a site-wide banner for manage.get.gov that can be easily pulled as needed. We should create a boilerplate site-wide banner that can be customized to address any issues that may result when registrar features are unavailable

Acceptance criteria

• Implement a site-wide banner for display on manage.get.gov when registrar is malfunctioning or has limited capabilities, based on banners in get.gov.
• Recycle (re-use from get.gov) content for boilerplate banner for use on manage.get.gov. Inside the banner, have date/time placeholder. Two banners to be made:
  • maintenance mode
  • degraded performance
• Design has reviewed and provided input after changes made (ping @Katherine-Osos directly)
• update our incident instructions with how to put up and remove this banner

Additional context

No response

Links to other issues

Related to:

• Design banner to inform users/analysts when the registrar (manage.get.gov) is unavailable get.gov#226
• Django Admin: Banner (or other notification) when the registry is down #1165
• Design: create page-specific banners for manage.get.gov #2495