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`fast/stages/2-networking-a-simple`: The stage is being deprecated, and superseded the `2-networking` FAST stage, introduced in #3435
`fast/stages/2-networking-b-nva`: The stage is being deprecated, and superseded the `2-networking` FAST stage, introduced in #3435
`fast/stages/2-networking-c-separate-envs`: The stage is being deprecated, and superseded the `2-networking` FAST stage, introduced in #3435
`modules/net-vpc-factory`: The module has been deprecated, and superseded the `2-networking` FAST stage, introduced in #3435
```
