Catch all the exceptions and return the expected error format
See https://github.com/huggingface/datasets/issues/4596.

The endpoint https://datasets-server.huggingface.co/splits?dataset=universal_dependencies returns:

```
Internal Server Error
```

instead of a JSON.

It results in moon-landing showing a weird and unrelated error (it expects a JSON, it gets a text content):

> invalid json response body at https://datasets-server.huggingface.co/splits?dataset=universal_dependencies reason: Unexpected token I in JSON at position 0

<img width="804" alt="Capture d’écran 2022-07-18 à 11 55 26" src="https://user-images.githubusercontent.com/1676121/179552382-2218bf9e-9a7e-4552-8440-428632f574fe.png">



Catch all the exceptions and return the expected error format: See https://github.com/huggingface/datasets/issues/4596.

The endpoint https://datasets-server.huggingface.co/splits?dataset=universal_dependencies returns:

```
Internal Server Error
```

instead of a JSON.

It results in moon-landing showing a weird and unrelated error (it expects a JSON, it gets a text content):

> invalid json response body at https://datasets-server.huggingface.co/splits?dataset=universal_dependencies reason: Unexpected token I in JSON at position 0

<img width="804" alt="Capture d’écran 2022-07-18 à 11 55 26" src="https://user-images.githubusercontent.com/1676121/179552382-2218bf9e-9a7e-4552-8440-428632f574fe.png">


