[FEATURE]: Refactor the rest of the backend training endpoints to /training

[dwu359]

Feature Name

Refactor the rest of the backend training endpoints to /training

Your Name

Daniel Wu

Description

Add endpoints to /training so that:

• /image trains an image model
• /object-detection trains an object detection model
• /classical-ml trains a classical-ML model

Make sure to update, reuse, and/or add any classes in /core as necessary

### Tasks
- [ ] https://github.com/DSGT-DLP/Deep-Learning-Playground/issues/993
- [ ] https://github.com/DSGT-DLP/Deep-Learning-Playground/issues/994
- [ ] https://github.com/DSGT-DLP/Deep-Learning-Playground/issues/750

[github-actions[bot]]

Hello @dwu359! Thank you for submitting the Feature Request Form. We appreciate your contribution. :wave:

We will look into it and provide a response as soon as possible.

To work on this feature request, you can follow these branch setup instructions:

1. Checkout the main branch:

```
 git checkout nextjs
```

2. Pull the latest changes from the remote main branch:

```
 git pull origin nextjs
```

3. Create a new branch specific to this feature request using the issue number:

```
 git checkout -b feature-908
```

Feel free to make the necessary changes in this branch and submit a pull request when you're ready.

Best regards, Deep Learning Playground (DLP) Team