handle price of food

[Xantass]

Describe your changes

The back should be able to receive the price of each food when an order is being sent on the POST route /orders/
When the order is received, the sum of all of the food's prices needs be store in the 'total' row of the order. This also include when the order is being updated (when a new food is added after the order was first sended)

How to test the feature

Add new order and check if the total field is ok
Update an order and check if the total field was modified correctly

Issue ticket number and link

#115

Checklist before requesting a review

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have performed a self-review of my code
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Documentation has been updated as required
  If a single item in this checklist is not checked, the pull request cannot be accepted