feat: app --region support to metrics collector script

[andy-townsend]

Issue #, if available:

Current script defaults to scanning 17 regions which for us fails due to IAM permissions. We noticed it only got as far as 12 regions and then quit so this PR adds a --region flag to allow scanning of a single region.

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[tebanieo]

Create first a constant that includes all the regions.

AWS_REGIONS = [
    "us-east-1", "us-east-2", "us-west-1", "us-west-2",
    "ca-central-1", "eu-west-1", "eu-west-2", "eu-west-3", 
    "eu-central-1", "eu-north-1", "eu-south-1", "ap-south-1",
    "ap-northeast-1", "ap-northeast-2", "ap-northeast-3", 
    "ap-southeast-1", "ap-southeast-2", "ap-southeast-3",
    "sa-east-1", "me-south-1", "af-south-1"
]

Create a validation function

def is_valid_aws_region(region):
    return region in AWS_REGIONS

def validate_aws_region(region):
    if not is_valid_aws_region(region):
        raise argparse.ArgumentTypeError(f"Invalid AWS region: {region}")
    return region

And then add this to the arg parsing.

parser.add_argument('--region', '-r', required=False,
                        type=validate_aws_region,
                        help='AWS region to use')

[tebanieo]

Thanks for your contribution, could you add the small change I requested? this will save errors before calling the AWS SDK.