Add subplan support for Security Center resource types to adjust the pricing model

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## Description
Some security center resource type like virtual machines or storage account can be customised with a subplan to adjust the pricing of that service.

As of today the following subplan are supported:

- Storage accounts ("PerStorageAccount")
- VirtualMachines ("P1" or "P2")

In the current implementation there is a boolean value to enable or disable the service.

```hcl
// Management resources
deploy_management_resources = true
configure_management_resources = {
advanced = null
location = ""
settings = {
log_analytics = {
# removed for clarity
}
security_center = {
config = {
email_security_contact = "email@domain.com"
enable_defender_for_app_services = true
enable_defender_for_arm = true
enable_defender_for_containers = true
enable_defender_for_dns = true
enable_defender_for_key_vault = true
enable_defender_for_oss_databases = true
enable_defender_for_servers = true
enable_defender_for_sql_server_vms = true
enable_defender_for_sql_servers = true
enable_defender_for_storage = true
}
enabled = true
}
}
tags = null
}
```

### Describe the solution you'd like

Customise the pricing at the platform landingzone level
Customise the pricing at the landingzone or sub-level

### Additional context

Start with the security_center configuration shown in the issue and review how its boolean resource settings are represented. Identify the supported Storage accounts and VirtualMachines subplan values, then verify that pricing can be customized at the platform landing zone and landing zone sub-levels.

Written by the indexing model from the issue text.