Inconsistent pattern for AWS::Backup::BackupSelection BackupSelection.SelectionName property in eu-central-1

Hi,

I noticed the pattern requirement for the `BackupSelection.SelectionName` property of the `AWS::Backup::BackupSelection` resource in `eu-central-1` is different to other regions.

The schema definitions for this property are as follows:

eu-central-1
```
"SelectionName" : {
"type" : "string",
"pattern" : "^[a-zA-Z0-9\\-\\_\\.]{1,50}$"
}
```

us-west-1
```
"SelectionName" : {
"type" : "string"
}
```

ap-southeast-2
```
"SelectionName" : {
"type" : "string"
}
```

Other regions appear to be consistent with `us-west-1` and `ap-southeast-2`, having no pattern requirement.

The impact of this is that we cannot deploy `BackupSelection` resources in eu-central-1 with the same `SelectionName` as those in other regions. I think the schema in `eu-central-1` must have been changed recently because we still have stacks deployed there which violate the pattern, we're unable to update those stacks without modifying the `SelectionName`.

Compare the regional schema definitions shown in the issue for AWS::Backup::BackupSelection.SelectionName, starting with eu-central-1 and the other listed regions. Confirm the intended pattern behavior and update the regional schema so existing stacks can be updated without changing SelectionName; verify the definitions remain consistent across regions.

Written by the indexing model from the issue text.