Add brands property to product API documentation

[gigitux]

This PR updates the documentation, adding details for the brands property:

• Introduced brands attribute in the product API, allowing for an array of brand objects with id, name, and slug.
• Updated examples to include brands in both request and response formats.
• Added a new section detailing Brands Properties for clarity.

Testing Instructions:

• Fetch a product with brands assigned -> GET /wp-json/wc/v3/products/:productId
• Ensure that the brands fields have this structure:

brands: [{
    "id": number,
    "name" string,
    "slug": string
}]

• Ensure that you can update brands assigned to the product via POST /wp-json/wc/v3/products/:productId passing:

brands: [{id:number}]

[Aljullu]

LGTM, thanks for noticing and fixing this, @gigitux! I left one small suggestion about capitalizing the name property, but not a blocker. 🚢

[Aljullu]

Not a big deal, but I see in the attributes, the name property is capitalized:

I think it's nice to make it clear it's a formatted text instead of a slug in snake-case.

[gigitux]

It makes sense! Thanks for the review! Fixed with da0cdb0