Improvement/Ui: Make network mode mandatory or validate when creating vpc offering and network offering

### The required feature described as a wish

As a Admin/Operator I would like to see if the particular vpc or network offering is natted or routed

If the admin user doesn't select the network mode , identifying if the offering is routed or natted is difficult

https://cloudstack.apache.org/api/apidocs-4.22/apis/createVPCOffering.html
https://cloudstack.apache.org/api/apidocs-4.22/apis/createNetworkOffering.html

https://cloudstack.apache.org/api/apidocs-4.22/apis/listVPCOfferings.html
https://cloudstack.apache.org/api/apidocs-4.22/apis/listNetworkOfferings.html

Currently, we support the creation of vpc offering without selecting the network mode

Select Natted mode when creating vpc offering > Check the details > natted mode is mentioned

Similarly, for network offerings, cloudstack shows natted mode only when the admin user selects the network mode