[BUG] No path for cookies can be provided in $cookies.set

[fsavina]

We're experiencing some severe problems related to the fact that there's no path provided to the $cookies.set function.
https://github.com/vuestorefront/shopware-pwa/blob/master/packages/nuxt-module/plugins/api-client.js#L34

For example, if a user arrives on the website through a direct link to a category page (e.g. via google serp), the cookies will be set on the current path (e.g. /main-category/sub-category).

The user then adds a product to the cart (which is connected to his context) and leaves the website after that.
If the user comes back and access the website through a different page the cookies won't be found, therefore causing the code to set new cookies for the current path (and a new context in SW).

The first context is then lost for all the pages other than /main-category/sub-category and its subpages.

The tokens should be set with path='/' to avoid all this.