feat: enhance network interface configuration with multiple secondary…

[Chaaany]

… ENIs support

Fixes: #156
Related: #156
Merge before/after: None
feat: enhance network interface configuration with multiple secondary ENIs support

Description
This PR implements comprehensive support for multiple Secondary ENIs with the following changes:

1. Code Changes:

• Modify CreateNewLaunchTemplate to handle multiple secondary ENIs
• Update RegionConfig struct to use slice for secondary ENIs
• Add validation logic for ENI configurations
• Extract security group validation into a separate public method ValidateSecurityGroupsConfig
• Ensure mutual exclusivity between ENI and non-ENI security group configurations

2. Testing:

• Add TestValidateSecurityGroupsConfig for security group validation
• Test cases cover:
  • Valid security groups without ENI
  • Invalid security group format
  • Empty security groups without ENI
  • Valid ENI with security groups
  • ENI without security groups
  • Both security groups and ENI specified
  • Secondary ENI without security groups
• Verify backward compatibility

3. Documentation:

• Add Network Interface Configuration section to README.MD
• Document three ways to configure security groups:
  • Using Launch Template Security Groups (Default)
  • Using Primary ENI Security Groups (Optional)
  • Using Multiple ENIs with Security Groups (Optional)
• Clarify mutual exclusivity between ENI and non-ENI security group configurations
• Document all network interface parameters and their usage
• Add examples for various configuration scenarios

The changes follow AWS best practices for ENI configuration and ensure that users can safely configure multiple network interfaces for their instances. The implementation maintains backward compatibility while adding new functionality.

Security Group Configuration Examples

1. Using Launch Template Security Groups (Default):

security_groups:
  - sg-12345678

2. Using Primary ENI Security Groups (Optional):

primary_eni:
  device_index: 0
  subnet_id: subnet-12345678
  security_groups:
    - sg-12345678

3. Using Multiple ENIs with Security Groups (Optional):

primary_eni:
  device_index: 0
  subnet_id: subnet-12345678
  security_groups:
    - sg-12345678

secondary_enis:
  - device_index: 1
    subnet_id: subnet-87654321
    security_groups:
      - sg-87654321
    private_ip_address: 10.0.1.100
  - device_index: 2
    subnet_id: subnet-87654321
    security_groups:
      - sg-87654321
    private_ip_address: 10.0.1.101

Follow-up Work

• Consider adding support for ENI tagging
• Add validation for subnet CIDR range compatibility
• Consider adding support for ENI attachment order configuration
• Add more comprehensive examples for complex network setups

[YoungJinJung]

LGTM