Upload document files to S3

[Ashesh3]

Fixes #61

This PR updates the file upload functionality in Django to use Amazon S3 for storage. This change provides several benefits, including improved scalability, durability, and availability of uploaded files.

The following changes were made to implement this feature:

• Added the boto3 library to requirements.txt for interacting with S3.
• Configured the AWS credentials and S3 bucket name in the Django settings file.
• Updated the file upload view to use the boto3 library to upload the file to S3.
• Updated the file model to store the S3 object key instead of the file path.