AWS::EC2::SecurityGroup GetAtt for GroupName

Please add a new attribute to SecurityGroups for the group's name. When creating SGs and letting CFN generate the name, there is no way to get this group name.

## Expected

```yaml
!GetAtt MySG.GroupName
```

## Links

https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-properties-ec2-security-group.html

## Category

4. Networking & Content (VPC, Route53, API GW,...)

Start by reading the AWS::EC2::SecurityGroup documentation linked in the issue and reviewing the requested !GetAtt MySG.GroupName example. Confirm how CloudFormation exposes SecurityGroup attributes when it generates the group name. Done means the GroupName attribute is supported and returns the generated security-group name.

Written by the indexing model from the issue text.