Add `product_categories` to metric and event definitions

Problem

Problem described in Re-Introduce metric / event to product_category... (&14553 - closed)

Desired outcome

product_categories is available as a field in metric and event definitions.

Proposed Solution

• The generator allows filling the field similar to the group field.
• The field itself is an array to account for the fact that a single feature, and thereby possibly a single event/metric, can be attached to multiple categories (example)

How to verify

Create a new event/metric combination, product category should be available to choose and be filled.

Follow up after

Make sure the data team adds the new field to the metric definition tables in Snowflake