Remove raw SQL usage from the codebase

[tobyash86]

There are some raw SQL queries in the code. We should consider using EF Core instead.
For some reason EF does not work properly in the checkout, we need to find out why and fix it.

[tobyash86]

The issue causes an exception when two exactly the same products are added to the cart.

The bug exists due to the fact that we call SQL manually to populate tables during checkout. We generate SQL with the same keys twice for the same products.

[tobyash86]

It seems like fixing the cart did not help with removing raw SQL. The main issue still exists.

[tobyash86]

Fixed. Requires verification on dev branch.