Feature: For enterprise deployments accept VNET, Subnet etc. as input parameters

### Feature or Idea - What?

Add 4 parameters:
VNET ID
Subnet ID
NSG ID
Route Table ID

If this parameters are set, the deployment won't create the VNET, instead it will use a VNET provided by Landing Zone team.

### Feature or Idea - Why?

For the Landing zone team, the data management landing zone is just an application landing zone.
They provide to the data team, a subscription, a vnet peered to the main network attached to a security group, etc. We want the deployment to be aware of that VNET; hence the addition of parameters.

Usually the DATA team does not have the rights to peer the VNET, or know the address scope,etc. That is why the Landing Zone provides this.

See:
https://docs.microsoft.com/fi-fi/azure/cloud-adoption-framework/ready/landing-zone/?WT.mc_id=modinfra-26634-salean#azure-landing-zone-conceptual-architecture

### Code of Conduct

- [X] I agree to follow this project's [Code of Conduct](https://github.com/Azure/data-management-zone/blob/main/CODE_OF_CONDUCT.md)