Render a 'wiki not enabled' page instead of a 404 if a project's wiki is not enabled (or has been disabled)

Description

When attempting to access a wiki for a project that has not been enabled OR was enabled and then disabled, a 404 is rendered.

Proposal

I feel instead of rendering a 404, we should render a 'this project does not have the wiki enabled' page.

Design

Draft, use the following text (not what appears in the illustration)

• Title: "This project does not have a wiki"
• Description: "Wiki is not enabled for this project. If you want to suggest adding a wiki, please contact the project owners via an issue in the issue tracker."
• Button: "New issue"