Add django-storages[boto3] to requirements.txt for S3 media storage support

[vvpoglazov]

Context

DefectDojo doesn't include django-storages in its dependencies, making it impossible to configure S3 as a media storage backend without maintaining a custom Docker image.

boto3 is already in requirements.txt, so django-storages[boto3] is a natural addition.

Proposed changes

• Add django-storages[boto3] to requirements.txt
• Add environment variables to settings.dist.py
• Add helm chart values for s3 configuration

I am willing to submit a PR for this.