gcommerce-8.x-1.0-beta5/modules/gcommerce_product/gcommerce_product.links.action.yml

group_relationship.group_product_add_page:
  route_name: 'entity.group_relationship.group_product_add_page'
  title: 'Add existing product'
  appears_on:
    - 'view.group_products.page_1'

group_relationship.group_product_create_page:
  route_name: 'entity.group_relationship.group_product_create_page'
  title: 'Add new product'
  appears_on:
    - 'view.group_products.page_1'