Add support for nested security group in security group definition.

[Nareshcbit]

Is your feature request related to a problem? Please describe.

In NSX a security group can have other security groups as its members. However, Terraform doesn't support it. Currently, it allows only VirtualMachine, VirtualNetworkInterface, CloudNativeServiceInstance, or PhysicalServer as members.

Describe the solution you'd like

Allow "SecurityGroup" as member_type for external_id_expression criteria in nsxt_policy_group_definition

resource "nsxt_policy_group" "group1" { display_name = "tf-group1" description = "Terraform provisioned Group" criteria { external_id_expression { member_type = "SecurityGroup" external_ids = ["520ba7b0-d9f8-87b1-6f44-15bbeb7935c7", "52748a9e-d61d-e29b-d54b-07f169ff0ee8-4000"] } }

Describe alternatives you've considered

There is no alternative to achieve it through Terraform

Additional context