Harden asset checkout validation

[marcusmoore]

Description

This PR follows up the reverted #15892 and adds the numeric and nullable rules for assigned_user, assigned_asset, and assigned_location.

The previous PR broke asset checkouts via the UI because the added rules didn't include nullable so validation failed since the UI includes the assigned_user, assigned_asset, and assigned_location fields in the submission. I amended the test to account for that.

Type of change

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

[what-the-diff]

PR Summary

• Improved Data Validation:
  • The rules that check and confirm the validity of data in our system have been made better. This change affects the way the system checks users, assets, and location specifications. This update includes more robust checks including numerical values and empty spaces.
• Enhanced Test Preparation:
  • We've updated our automatic system testing setup. We've created a list of default properties including user, asset, and location that will always be integrated during the testing process.
  • This setup also merges these default properties with the incoming new data. The benefit of this is that it makes our testing processes cleaner and more manageable.
• Consistent Data Format Changes:
  • The format of various properties - user, asset, and status identifiers - have been updated when sending or receiving data during the checkout process. This promotion of consistency helps in reducing errors and making our system function with more reliability.