AWS Batch support - MIME Multipart Userdata format compatibility

### Description
I'm trying to use the official ECS-optimized Bottlerocket AMI with AWS Batch but encountering compatibility issues that prevent instances from joining the ECS cluster.

### Environment
- **AMI**: `bottlerocket-aws-ecs-2-aarch64-v1.49.0-713f44ce`
- **Service**: AWS Batch
- **Architecture**: aarch64

### Problem
When using Bottlerocket AMI with AWS Batch the instances fail to join the ECS cluster, preventing tasks from running.

### Root Cause
AWS Batch expects user data in **MIME Multipart format**, while Bottlerocket uses **TOML configuration format**. This incompatibility causes the Bottlerocket startup script to fail during initialization, preventing the instance from successfully joining the ECS cluster.

### Expected Behavior
Bottlerocket instances should be able to process MIME Multipart user data format for enhanced configuration abilities

### Proposed Solution
Add support for parsing and handling MIME Multipart user data format alongside the existing TOML configuration format, or provide a compatibility layer that can extract and process Bottlerocket-specific configuration from MIME Multipart user data.

### Use Case
This would enable Bottlerocket to be used with AWS Batch for security and performance