This PR (re :D)introduces module net-vpc-factory, a minimal factory that deals with vpcs, subnets, and firewall rules creation, meant to be embedded into other factories, starting with 2-data-platform and 2-networking.
This PR renames `2-networking-foo` stages to `2-networking-legacy-foo` - including references of stages in docs and tests.
**Breaking Changes**
```upgrade-note
`fast/stages/2-networking-a-simple`: The stage is being deprecated, and superseded the `2-networking` FAST stage, introduced in #3435
`fast/stages/2-networking-b-nva`: The stage is being deprecated, and superseded the `2-networking` FAST stage, introduced in #3435
`fast/stages/2-networking-c-separate-envs`: The stage is being deprecated, and superseded the `2-networking` FAST stage, introduced in #3435
`modules/net-vpc-factory`: The module has been deprecated, and superseded the `2-networking` FAST stage, introduced in #3435
```
This pull request introduces the `net-vpc-factory` module. This new factory handles:
* Project setup (most of what's supported by the `project` module)
* VPC setup
* Routing
* Subnets
* Connectivity options
* NCC (hub, VPC spokes and VPN hybrid spokes)
* Peerings
* VPN (GCP-to-onprem and GCP-to-GCP)
* NAT (everything supported by the `net-cloudnat` module)
* DNS (everything supported by the `dns` module)
* Firewall (everything supported by the `net-vpc-firewall` module)
