[ENH] - UI messaging for when a user is unable to start shared app

[aktech]

Feature description

We would need to handle the case when a shared app is stopped and the person with whom the app is shared, tried to access the app and then start it, in that case "starting the app" will fail. At the moment backend returns 404.

We're not allowing the shared user to start the app and in future we may, in that case it will return either 200 or 403.

So to summarise we need to handle the following cases:

• 200 (already handled)
• 404, 403: The error message should be something like you don't have permissions to start user "original-author"'s app, please ask the app author to start the app. (Same error for both cases since we're not allowing app starts by non-author for now)
• 500: Something went wrong, generic error.

The later two cases are not handled at the moment. I am happy to get this PR in and handle those in a follow up PR as this is a huge improvement anyway.

Value and/or benefit

Better visibility for the user when they tried to start an app they don't have permissions to.

Anything else?

No response