No visible error when creating content not defined in `content.config.ts`

[stijns96]

Is your feature request related to a problem? Please describe

I'm trying to create a file that is not defined in my content.config.ts, but don't get any visible error. Looking at the console, I'm getting

host.js?v=16e9f590:145 Uncaught (in promise) Error: Collection not found for fsPath: test.yaml
    at Object.get (host.js?v=16e9f590:145:19)
    at Object.create (host.js?v=16e9f590:173:59)
    at create-document (main.js?v=16e9f590:13127:76)
    at Object.handler (main.js?v=16e9f590:13116:82)
    at Proxy._10 (main.js?v=16e9f590:15860:23)
    at j10 (main.js?v=16e9f590:13790:93)

Describe the solution you'd like

A simple toast mentioning you can't create a file that is not defined in the content.config.ts. Would be good to make this error understandible for editors/clients as well. Maybe it would be even nice if we could override error messages with our own messages.