Fortigate configuration: VM in mgmt vpc/subnet can have internet access without using a NAT? The reconfigured fortigate 4th mgmt NIC can not be used for firewall policies

see #446

Discussion around allowing for internet update access from VMs in the management subnet of the fortigate example 4 nic LB sandwich HA active/passive architecture.

#158
https://github.com/fortinet/fortigate-tutorial-gcp

tracking add kcc version of fortigate-tutorial-gcp (collaboration PR) https://github.com/fortinet/fortigate-tutorial-gcp/issues/5

https://github.com/GoogleCloudPlatform/pubsec-declarative-toolkit/blob/dev/solutions/landing-zone/architecture.md#fortigate-ha-active-standby-poc

Currently one of our architects is prototyping exporting the logs from the fortigate active VM into a VM in the mgmt VPC.
Issue looks to be switching the nic as a mgmt interface causes it not to be available for firewall policies.

Need to reproduce and put up a PR patch to work with
Need to check on GCP firewall rules override as an option

Quoting prior to reproduction
- use the following repo to create the Fortigate cluster 6 VPC deployment https://github.com/fortinet/fortigate-tutorial-gcp/issues/1

```
config system ha
set group-name "group1"
set mode a-p
set hbdev "port3" 50
set session-pickup enable
set ha-mgmt-status enable
config ha-mgmt interfaces
edit 1
set interface "port3"
set gateway ${hamgmt_gateway_ip}
next
end
set override enable
set priority 255
set unicast-hb enable
set unicast-hb-peerip ${passive_hb_ip}
set unicast-hb-netmask ${hb_netmask}
end
```