Add support to boto3 default connection

[Omarlsg98]

What problem does this PR solve?

This pull request includes changes to the initialization logic of the ChatModel and EmbeddingModel classes to enhance the handling of AWS credentials.

Use cases:

• Use env variables for credentials instead of managing them on the DB
• Easy connection when deploying on an AWS machine

Type of change

• [ ] Bug Fix (non-breaking change which fixes an issue)
• [X] New Feature (non-breaking change which adds functionality)
• [ ] Documentation Update
• [ ] Refactoring
• [ ] Performance Improvement
• [ ] Other (please describe):