[Docs] Dataset management updated

[juanferrub]

The changes enhance the documentation by providing a complete guide for creating datasets through the UI, complementing the existing SDK documentation.

Details

• Added a new section "Create a dataset via the UI" before the SDK section
• Added steps for creating datasets through the UI
• Added a screenshot of the UI (create_dataset.png)
• Added CSV format requirements
• Added a Tip section about UI limitations
• Fixed grammar ("a dictionary" instead of "dictionary")
• Fixed article usage ("create a dataset" instead of "create an dataset")
• Fixed bullet point formatting to use proper markdown syntax (* instead of • or -)
• Added guidance about when to use the UI vs SDK
• Added the image to the documentation with proper formatting