feat(API-1904): Add JS code snippets for GT "How to collect product variations" (#742)

* feat(API-1904): refactor snippet js get families variants

* feat(API-1904): add snippet js to how to collect product variations + refactor

* feat(API-1904): refactor maxItems to maxProductsPerPage in family variants snippet

Co-authored-by: Samuel Gomis <[email protected]>

Author: samokiss