[BUG]: Fix User endpoints and tests

[ssh51117]

Operating system

n/a

Bug description

Currently, the user DynamoDB endpoints are using a mix of @aws-sdk/client-dynamodb and @aws-sdk/lib-dyanmodb. We want to only use the client-dynamodb, since the lib is just a wrapper that calls the client behind the scenes to allow for a slightly prettier input.
Additionally, the unit tests have errors that can be suppressed for clarity.

Also need to update dyanmoDB and Vitest guides to reflect these changes.

Steps to reproduce

No response

[github-actions]

Hello @ssh51117! Thank you for submitting the 🐞Bug Request Form. We appreciate your contribution. 👋

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

To work on this bug 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 bug request using the issue number:
   git checkout -b bug-1159

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