Added machine learning endpoint for recommending categories for products

Introduced Machine Learning APIs to autonomously learn from data and make automated predictions. This reduces the amount of manual work required to manage projects.

The first machine learning API endpoint available is the Category Recommendations endpoint. The Category Recommendations endpoint suggests categories that best fit a given product. Further information on the background of this feature can be found on the tech blog.

• [API] Added public endpoints for the Category Recommendations feature.