Project Modal - Classifier dropdown

### Current Behavior

The classifier for a project shows as being mandatory, however there are two observed bugs with the current behavior

1. You can create a project without selecting a Classifier. No input validation error thrown to user. Defaults to `Application`

2. Selecting `None` as the `Classifier` has a green tick, but when creating throws a HTTP 500 Internal Server Error

### Steps to Reproduce

1. Create a new project
2. Leave Classifier blank, and/or, select `None` as Classifier

### Expected Behavior

User input handled

### Dependency-Track Frontend Version

4.13.0

### Browser

Google Chrome

### Browser Version

_No response_

### Operating System

macOS

### Checklist

- [x] I have read and understand the [contributing guidelines](https://github.com/DependencyTrack/dependency-track/blob/master/CONTRIBUTING.md#filing-issues)
- [x] I have checked the [existing issues](https://github.com/DependencyTrack/frontend/issues) for whether this defect was already reported