Better error responses in /apps endpoints

[fusion44]

Is your feature request related to a problem? Please describe.

Only a very generic internal server error is thrown when handling apps. Detail is not very in depth:

{
  "detail": "Unknown error"
}

Describe the solution you'd like

Provide a more descriptive error message

[fusion44]

@rootzoll This mostly has been you area, if you have some time to spare :D

[rootzoll]

Opened an reminer for v1.8.1 on raspiblitz repo: https://github.com/rootzoll/raspiblitz/issues/3318

[fusion44]

For me this is bigger change which is more suited for 1.9?

I've also removed the good first issue tag. This is an advanced change which requires knowledge of the RaspiBlitz base system and the API code.

[rootzoll]

For me this is bigger change which is more suited for 1.9?

what do you see for you to change here? I think its mostly up to me to deliver better error messages here.

[fusion44]

There's another issue which could be tackled at the same time:

https://github.com/fusion44/blitz_api/issues/123

The task would be to have a coherent error response policy. To assess this will take some time.