Hardened asset checkout validation by requiring integer

[marcusmoore]

Description

This PR adds integer to the rules for assigned_user, assigned_asset, and assigned_location when checking out an asset via the api. This is to avoid passing in an array or something else unexpected.

Type of change

• Bug fix (non-breaking change which fixes an issue)

[what-the-diff]

PR Summary

• Enhanced Validation Rules
  Updated the rules for verification of 'assigned_user', 'assigned_asset' and 'assigned_location'. Now, they need to be integer values. This step will likely improve the accuracy and correctness of the data input.