Add Datasets API with 8 datasets and demo notebooks

[karaposu]

Summary

• Datasets API: filter, download, export pre-collected data
• 8 datasets: LinkedIn (profiles/companies), Amazon, Crunchbase, IMDB, NBA, Goodreads, World Population
• Export utils: export_json, export_csv
• Demo notebooks for LinkedIn, Amazon, Crunchbase

Usage

async with BrightDataClient() as client:                                                                                          
    snapshot_id = await client.datasets.amazon_products(                                                                          
        filter={"name": "rating", "operator": ">=", "value": 4.5},                                                                
        records_limit=100                                                                                                         
    )                                                                                                                             
    data = await client.datasets.amazon_products.download(snapshot_id)                                                            
    export_json(data, "results.json")