Automatic merge from submit-queue (batch tested with PRs 48497, 48604, 48599, 48560, 48546)
GCE: Use network project id for firewall/route mgmt and zone listing
- Introduces a new environment variable for plumbing the network project id which will be used for firewall and route management. fixes#48515
- onXPN is determined by metadata if config is not specified
- Split `if` conditions: fixes#48521
- Remove `getNetworkNameViaAPICall` which was used as a last resort for the `networkURL` (if empty) which was previously filled with the metadata network project & name.
**Release note**:
```release-note
NONE
```
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