Parameter type 'List<AWS::EC2::Subnet::Id>' does not support AllowedPattern

### Name of the resource

Other

### Resource name

Parameters

### Description

We use `Parameters` with the type `List` to let customers specify which subnets to deploy the resources to.

However, we must require the customers to specify at least two subnets for subsequent deployment requirements.

### Other Details

After changing the type to `String`, it can validate the subnet size by regexp pattern. Still, we need the capability of the rule to validate the subnets in that VPC and the subnet selector in the CloudFormation console.

No repository files, tests, or entry points are identified in this coverage-roadmap request. Start by reviewing the issue requirements: list subnet parameters should support minimum-count validation while retaining subnet and VPC validation and the CloudFormation console selector; done means that capability is supported.

Written by the indexing model from the issue text.