Data Manager is not properly indexing data fields as columns.

**Describe the bug**
A clear and concise description of what the bug is.

I have a sample like so for NER:

```
{
"data": {
"text": "test",
"id": "194215",
"source_type": "query",
"possible_brands": "test2"
},
"predictions": [
{
"result": [
{
"from_name": "label",
"to_name": "text",
"type": "labels",
"value": {
"start": 0,
"end": 5,
"text": "test",
"labels": [
"TEST"
]
}
}
],
"score": 0.9999
}
]
}
```

When I import the tasks, none of the columns are appearing properly. The only columns I see are ID, Completed, the three annotation/prediction columns, and Annotated by.

When I click on a task and move to the annotation UI, that's where I see everything properly.

In the Data Manager, I tried clicking on Columns to make sure that nothing was unchecked by default, but I don't see any columns and on the very bottom I only see "data" in code font.

**To Reproduce**
Steps to reproduce the behavior:
1. Go to '...'
2. Click on '....'
3. Scroll down to '....'
4. See error

**Expected behavior**
A clear and concise description of what you expected to happen.

**Screenshots**
If applicable, add screenshots to help explain your problem.

**Environment (please complete the following information):**
- OS: [e.g. iOS]
- Label Studio Version [e.g. 0.8.0] v1.15.50

**Additional context**
Add any other context about the problem here.