fix(vpc): avoid deprecated numeric_id warning in network output

[bruno561]

This PR addresses #706 by removing the deprecation warning triggered by the network output in the VPC submodule.

Previously, the output returned the full google_compute_network.network resource object, which surfaces a deprecated provider attribute (numeric_id) during validation.
This change replaces that with an explicit object of selected stable attributes.

Changes

• Updated modules/vpc/outputs.tf:

1. Replaced output "network" value from raw resource object to a selected attribute map.
2. Added network_id from google_compute_network.network.network_id.
3. Kept numeric_id as a compatibility alias mapped to network_id.
4. Updated modules/vpc/README.md output description for network to reflect the new shape.

Why this approach

• Removes dependency on deprecated provider internals in output evaluation.
• Preserves backward compatibility for consumers that still read network.numeric_id.
• Keeps the PR scope small and focused on deprecation cleanup.

Validation

• terraform init (in modules/vpc)
• terraform validate (in modules/vpc) -> Success

Closes #706