text: Title: Bug: Serializing TorchTensor with grad fails
  Body: **Description:**
  When a `TorchTensor` requires grad it cannot be serialized to JSON.
  This is particularly bad because:
  -  outputs of pytorch models require grad
  - FastAPI serilaizes to JSON
  -> model serving is b0rked
  
  **How to reproduce:**
  ```python
  from docarray import BaseDoc
  from docarray.typing import TorchTensor
  import torch
  
  class MyDoc(BaseDoc):
      tens: TorchTensor
  
  t1 = torch.rand(512, requires_grad=True)
  doc = MyDoc(tens=t1)
  doc.json()
  ```
  ```bash
  TypeError: Type is not JSON serializable: TorchTensor
  ```
  
  But the following works:
  ```python
  from docarray import BaseDoc
  from docarray.typing import TorchTensor
  import torch
  
  class MyDoc(BaseDoc):
      tens: TorchTensor
  
  t1 = torch.rand(512, requires_grad=True)
  doc = MyDoc(tens=t1.detach())
  doc.json()
  ```
  
  **TODO**:
  - Fix this, probably by calling `detach()` in the serialization logic
  - check if other serialization options are also affected
  - what about tensorflow?