[S3] Update S3 bucket and the fetching secrets method

[cyaiox]

🎉 Description

There's a new S3 bucket for the builder server that uses CloudFront. This new mechanism will allow us to save money as cloudfront can cache the request more cost-effectively than serving content directly from S3.

Tasks:

• [ ] Update S3 bucket URL to: https://builder-assetspack.decentraland.org/
• [ ] Fetch the new credentials using aws secrets manager