Implement /credentials/shop/ as flask view

[britneywwc]

Done

• Removed /credentials/shop/ that was previously a React app and implement in flask view

QA

• Go to demo shop
• Purchase an exam
• Should redirect to the checkout page with the correct exam & price
• Check that it works exactly like the live version

Issue / Card

Fixes WD-8193

Help

QA steps - Commit guidelines

[webteam-app]

Demo starting at https://ubuntu-com-13464.demos.haus

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 74.41%. Comparing base (e93384d) to head (b0d2d01).
Report is 3 commits behind head on main.

❗ Current head b0d2d01 differs from pull request most recent head c8ff6e0

Please upload reports for the commit c8ff6e0 to get more accurate results.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #13464      +/-   ##
==========================================
+ Coverage   74.12%   74.41%   +0.29%     
==========================================
  Files         107      107              
  Lines        2864     2838      -26     
  Branches      957      946      -11     
==========================================
- Hits         2123     2112      -11     
+ Misses        715      702      -13     
+ Partials       26       24       -2     

see 12 files with indirect coverage changes