Provide guest user authentication

[kidunot89]

Describe the bug
Cart items for guest users have no way of being persisted. This is due to the fact that there is current no way to identifying individual guest users client-side.

To Reproduce
Steps to reproduce the behavior:

1. Add an item to the cart using a cart mutation
2. Refresh the browser page
3. Query the cart

Expected behavior
Cart items should be persisted between request.

[jake-101]

How do you login as a guest or create a session. It requires JWT?

[kidunot89]

See #88