refactor: switch ec2 deploy logic from BCP_BUCKET to S3_BUCKET

[l50]

Key Changes:

• Replaced all usage of BCP_BUCKET with S3_BUCKET for staging and deployment
• Simplified S3 bucket configuration by removing auto-detection from bcp config
• Updated precondition and error messages to reference S3_BUCKET instead of BCP_BUCKET

Changed:

• S3 bucket configuration now uses S3_BUCKET as a required variable, eliminating the previous BCP_BUCKET auto-detection logic and related shell scripting
• All S3 upload and download commands updated to use S3_BUCKET instead of BCP_BUCKET throughout the EC2 Taskfile deployment and config tasks
• Preconditions and error messages revised to refer to S3_BUCKET, providing clearer guidance on how to set the required variable