[Product Block Editor] Add post_password parameter to the Woo product REST api

[louwie17]

As part of #38823 we are creating a new tab that includes a product password field, to protect the product.

Currently the WooCommerce REST api does not have support for a password field, and this can only be accessible by using the core data store for posts.
We should add support for this by adding a post_password property, as the WC_Product class already has the logic in place for this, see: $product->get_post_password( $context ); and set_post_password.

It is fine to add this as part of version3

Acceptance criteria

• WooCommerce API should expose a post_password param as part of the data
• WooCommerce API should allow us to update the post_password field.