Backend: Add get orders (by user) endpoint

[JiuTak]

Description

Please provide a short summary explaining what this PR is about.

Fixes #99

How to test?

localhost:3000/api/documentation

Check ORDERS

Checklist

• [x] I have performed a self-review of my own code
• [x] I have followed the name conventions for CSS Classnames and filenames, Components names and filenames, Style filenames, if you are in doubt check the the project README.MD and here https://github.com/HackYourFuture-CPH/curriculum/blob/master/review/review-checklist.md
• [x] I have commented my code, particularly in hard-to-understand areas, if you code was simple enough mark the box anyway
• [x] I have made corresponding changes to the documentation, if you code was simple enough mark the box anyway
• [x] This PR is ready to be merged and not breaking any other functionality

[miltonhultgren]

@NataliaS1994 @JiuTak How can you share the code for the selection part in a good way, think about what kind of function you could extract to import into both controllers for sharing that logic :)

[miltonhultgren]

I'd update the PR title and merge commit message to: Add get orders (by user) endpoint