Update autoscaling config to use metrics_providers

[ernestosilv]

This PR updates the script to handle the new autoscaling configuration format, which now uses a list of metrics_providers instead of a single metrics_provider. The following changes were made:

• Modified the script to construct the instance_config with a metrics_providers list.
• Ensured that the metrics_provider and setpoint are added as dictionaries within the metrics_providers list.
• Updated the handling of the autoscaling configuration to match the new format specified in the provided config file.

These changes address the recent update in the autoscaling configuration format, ensuring that the script correctly handles the new structure.