Feature/estimated order amount update product

[dpanta94]

All Submissions:

• [x] Does your code follow the Extendables standards?
• [ ] Have you written new tests for your changes, as applicable?
• [x] Have you successfully run tests with your changes locally?

Changes proposed in this Pull Request:

Adds the estimated order amount in every place available by the plugin.

How to test the changes in this Pull Request:

1. Estimated order amount should be added on all the cases the plugin provides for checkout.
2. Classic gateway: checkout and order-pay
3. Express gateway: cart, checkout, order-pay, mini-cart, single product

Other information:

• [x] Have you checked to ensure there aren't other open Pull Requests for the same update/change?