Missing PolicySubType (Enhanced, Standard) on 'Microsoft.RecoveryServices/vaults/backupPolicies'

**Bicep version**
0.14.0

**Describe the bug**

When creating a Backup Policy, it defaults to 'Standard' as the policy sub type. There is no option for creating a Enhanced Backup Policy through Bicep. [Documentation](https://learn.microsoft.com/en-gb/azure/templates/microsoft.recoveryservices/vaults/backuppolicies?tabs=bicep&pivots=deployment-language-bicep)

**To Reproduce**
This step doesn't make sense in this context.

**Additional context**

An Enhanced Backup Policy is needed to backup trusted launch VM's and cannot use the Standard Policy. In addition, it cannot be created through the az cli either. The az has a list function with subtype but create has none:

```
az backup policy list --resource-group
--vault-name
[--policy-sub-type {Enhanced, Standard}]
```

```
az backup policy create --backup-management-type {AzureIaasVM, AzureStorage, AzureWorkload}
```

[documentation](https://learn.microsoft.com/en-us/cli/azure/backup/policy?view=azure-cli-latest#az-backup-policy-create)

This is a bug report because the Bicep template is missing a key component in order to create backup policies as IaaC. If, however, it is a feature request, let me know.

Start with the Microsoft.RecoveryServices/vaults/backupPolicies Bicep resource documentation and the repository's corresponding resource type definition, then compare it with the documented az backup policy list and create commands. Confirm where PolicySubType is represented and verify that both Enhanced and Standard backup policies can be expressed through the generated Bicep type.

Written by the indexing model from the issue text.