Add and Delete Management Subinterfaces

Use the EFA CLI to add and delete management subinterfaces.

Run the following command to add a management subinterface:
```
efa mgmt subinterface create --name <name> --ip-address <ip-subnet> 
--vlan-id <VLAN>
```
- If a management network with the same name exists, the operation fails.
- The changes made by this operation span three different components:
  - Subinterface creation under the physical NIC
  - Keepalived configuration changes (for high-availability deployments)
  - Ingress controller changes
- If any operation to the component fails, it is marked as a failed operation and the configurations return to the previous state.
Run the following commands to delete a management subinterface:
```
efa mgmt subinterface delete --name <name>
```
If a management network with the name exists, it is deleted. Otherwise, the correct response is provided in the command output.

Example

$ efa mgmt subinterface?
Management subinterface commands

Usage:
  efa mgmt subinterface [command]

Available Commands:
  create        Create sub-interface (sub-interface)
  delete        Delete sub-interface (sub-interface)
  show          List of sub-interfaces (sub-interfaces)

Flags:
  -h, --help          help for sub-interface

Use "efa mgmt subinterface [command] --help" for more information about a command.

$ efa mgmt subinterface create -h
Create management subinterface (sub-interface)
Usage:
  efa mgmt subinterface create [flags]
Flags:
      --name string         Name of the sub-interface
      --vlan-id int         VLAN Id of sub-interface
      --ip-address string   IP Address of sub-interface including subnet mask. 
                            Example: 10.24.80.150/24
  -h, --help                help for create

$ efa subinterface delete -h
Delete management subinterface (sub-interface)
Usage:
  efa mgmt subinterface delete [flags]
Flags:
      --name string   Name of the sub-interface
  -h, --help          help for delete

$ efa mgmt subinterface show -h
List of management sub-interfaces (sub-interfaces)

Usage:
  efa mgmt subinterface show [flags]
 Flags:
       --name string   Name of the sub-interface
   -h, --help          help for show

$ efa mgmt subinterface create --name server1 --vlan-id 20 --ip-address
          20.20.20.2/24
Subinterface server1 created successfully

$ efa mgmt subinterface delete --name server1
Subinterface server1 deleted successfully

$ efa mgmt subinterface show
+---------------+------------------+------+---------------+
| Sub-Interface | Parent Interface | Vlan |   IP Subnet   |
+---------------+------------------+------+---------------+
| server1       | eth0             | 20   | 20.20.20.2/24 |
+---------------+------------------+------+---------------+
| server2       | eth0             | 50   | 50.50.50.2/24 |
+---------------+------------------+------+---------------+
Management Subinterfaces Details

$ efa mgmt subinterface show --name server1
+---------------+------------------+------+---------------+
| Sub-Interface | Parent Interface | Vlan |   IP Subnet   |
+---------------+------------------+------+---------------+
| server1       | eth0             | 20   | 20.20.20.2/24 |
+---------------+------------------+------+---------------+
Management Subinterface Details