NER Labeling: UI Performance issues with large task json files

**Describe the bug**
I'm uploading a ~ 1MB json file containing 21 tasks of around 50kB. These contain a larger text file of around 25kB with 10 to 15 Named-Entity-Recognition (NER) predictions. After uploading the file with the necessary config the UI responds very slowly. It can take up to ~30 seconds to open a task and even scrolling through the predicted document takes ~3 seconds.

**To Reproduce**
Create a large tasks.json file as input
Update config to deploy frontend NER labelling using tasks.json
Go to localhost UI

**Expected behavior**
The frontend components should have similar speeds to small 10KB json files.

**Environment**
label-studio==1.1.0
label-studio-converter==0.0.29

OS: macOS Big Sur
Safari Version 14.1.1 (16611.2.7.1.4) (64-bit))
2,4 GHz 8-Core Intel Core i9, 32 GB 2667 MHz DDR4