[PW-8341] Support for Sessions endpoint approach via API

[Fifciu]

Is your feature request related to a problem? Please describe. Currently, the part of integration for Magento2 native frontend supports /sessions endpoint and WebComponent v5. However, API endpoints remain unchanged and they still force old approach with WebComponent v4. So users using headless approach (Vue Storefront 2 users for example) cannot benefit from the newest Checkout API and WebComponent.

Describe the solution you'd like I would love to see a new endpoint for sessions API but the old flow should remain with us for a while.

Additional context Add any other context or screenshots about the feature request here. Could you please add here an estimation if you decide to take care of that? I am planning updating Vue Storefront integration to the newest version of the plugin and I wonder if I should wait for an update with Session endpoint support or go with what we have right now.