Added tests around license checkin

[marcusmoore]

This PR focuses on adding tests around checking in licenses via the UI but extracts a translation string along the way.

[what-the-diff]

PR Summary

• Improved Error Messaging

  • The error message shown for licenses that cannot be reassigned has been updated. It now uses a translatable string, meaning it can be displayed in various languages as needed.

• Better License Management

  • Two methods, reassignable and notReassignable, have been added to manage when licenses can or cannot be reassigned to different users or assets.

• Expanded Language Support

  • A new language line has been added for the non-reassignable error message, supporting the above change for translatable strings.

• More Robust Testing

  • New tests were added to ensure that the changes function as expected. These tests:
    • Confirm that attempting to check in a license that can't be reassigned triggers the correct error message.
    • Check that trying to check in an unassigned license also triggers the appropriate error message.
    • Validate that checking in licenses that are assigned to a user or asset works correctly.