Add data-hooks to admin/products/new and admin/products/_form

Similar to https://github.com/spree/spree/pull/4521, this commit adds data-hooks that make manipulation of the admin/products/new page considerably easier, cleaner, and more succinct.

Fixes #4682 and #4683

Conflicts:
	backend/app/views/spree/admin/products/_form.html.erb