Docs for creating a loading script for image datasets
_The documentation is not available anymore as the PR was closed or merged._ IMO it would make more sense to add a "Create image dataset" page with two main sections - a no-code approach with `imagefolder` + metadata (preferred way), and with a loading script (advanced). It should be clear when to choose which. If we leave this as-is, the user who jumps straight to the Vision section could be under the impression that writing a loading script is the preferred way to share a vision dataset due to how this subsection starts:
```
Write a dataset loading script to share a dataset.
```
  
Also, I think a note explaining how to make a dataset gated/disable the viewer to hide the data would be beneficial (it's pretty common to require submitting a form to access a CV dataset). Great suggestion @mariosasko! I added your suggestions, let me know what you think. For gated dataset access, I just added a tip referring users to the relevant docs since it's more of a Hub feature than `datasets` feature. Thanks, looks much better now :). I would also move the sections explaining how to create an `imagefolder` for the specific task from the [loading page](https://raw.githubusercontent.com/huggingface/datasets/main/docs/source/image_load.mdx) to this one. IMO it makes more sense to have the basic info (imagefolder structure + `load_dataset` call) there + a link to this page for info on how to create an image folder dataset. Good idea! Moved everything about `imagefolder` + metadata to the create an image dataset section since the `load_dataset` call is the same for different computer vision tasks.  Thanks for all the feedbacks! 🥰

What do you think about creating how to share an `ImageFolder` dataset in a separate PR? I think we should create a new section under `Vision` for how to share an image dataset. I love it thanks ! I think moving forward we can use CSV instead of JSON Lines in the docs ;)
This PR is a first draft of creating a loading script for image datasets. Feel free to let me know if there are any specificities I'm missing for this. 🙂 

To do:
- [x] Document how to create different configurations.