Add alert for disabled webhooks to all project pages

• Create a new feature flag to render a new Vue app in the projects layout app/views/layouts/project.html.haml (or similar).
• Make an API request to backend to check if the alert should be displayed or not.
• After the alert has been dismissed by a user, we should not show it again to them (persisted user callout functionality). This is usually stored in the backend as well.

Design source

✏ Figma project

Availability & Testing

Suggestions:

• add new feature spec to validate (please reach out to @sgregory2 for assistance)
  • that the alert is present after failing a webhook 4 times
  • that dismissing the alert and refreshing the page does not show the alert.
• run package-and-qa to ensure no tests break with and without the feature flag.