Add task tags for multimodal datasets
## **Is your feature request related to a problem? Please describe.**

Currently, task tags are either exclusively related to text or speech processing:
- https://github.com/huggingface/datasets/blob/master/src/datasets/utils/resources/tasks.json

## **Describe the solution you'd like**

We should also add tasks related to:
- multimodality
- image
- video

CC: @VictorSanh @lewtun @lhoestq @merveenoyan @SBrandeis 