adding input validation to application dates

[niclasheun]

This pull request includes several improvements and new features for the ApplicationConfigDialog component in the application administration section. The most important changes include adding new state variables, using useEffect to reinitialize form values, validating date and time input, and enhancing error handling.

State Management and Initialization:

• Added new state variables for endDate, startTime, endTime, externalStudentsAllowed, universityLoginAvailable, and dateError.
• Implemented useEffect to reinitialize form values when the dialog is opened or when initial data changes.

Validation:

• Added validation to ensure the start date and time come before the end date and time, and set an appropriate error message if the validation fails.

Error Handling:

• Created a new ApplicationConfigDialogError component to display error messages in a user-friendly manner.
• Updated the dialog to use the new ApplicationConfigDialogError component for displaying errors.

Code Improvements:

• Changed some imports to use type imports for better type safety and clarity.
• Refactored the handleSubmit function to build full Date objects by combining date and time values before submission.

These changes enhance the functionality, maintainability, and user experience of the ApplicationConfigDialog component.