[R5] Move/refactor Create Items API into ItemResource class

[wl2484]

As a developer I need to move/refactor Create Items API into ItemResource class So that Create Items API swagger doc would be available on the /apidocs page

Details and Assumptions

• Assumed the current Create Items API is implemented outside the ItemResource class.
• Assumed that ItemResource class is responsible for managing items and includes all item-related functionalities.
• Assumed the current Create Items API lacks a Swagger documentation, which needs to be added to the "/apidocs" page.

• Assumed that no functionality is lost during the move/refactor process.

  Acceptance Criteria

  
  Given the current implementation has a standalone Create Items API outside the ItemResource class.
  When the Create Items API is moved/refactored into the ItemResource class, and Swagger documentation is added.
  Then the Create Items API is now a part of the ItemResource class, and its functionality remains intact, 
  And the swagger documentation for the Create Items API is accessible and correctly displayed on the "/apidocs" page, 
  And testing is conducted to verify that the API works as expected and no new bugs are introduced during the refactoring process,
  And the refactored code is reviewed and approved by team members before merging it into master branch,
  And any dependent code that uses the Create Items API is updated to use the new location within the ItemResource class.

[nijya]

Hey team! Please add your planning poker estimate with Zenhub @emhao @LillisLuo @momo100110 @wl2484