Scope web-hook disabled banners to projects

Replaces !89471 (closed)

We need callouts for users telling them about recent web-hook failures in their projects. These will appear on project pages.

Each time a user visits a project pages we need to:

• see if there are new web-hook failures the user does not know about
• show them a banner to tell them
• hide the banner if they have dismissed it
• only show the banner to maintainers, who can do something about web-hooks

This issue is for the backend implementation of determining when to show the banner, which needs a new kind of callout that is scoped to a project.