feat: support bundle: automatically diagnose STUN issues in network support bundle

Part of https://github.com/coder/coder/issues/12160

The support bundle includes a netcheck report.
We can potentially automatically diagnose STUN issues by checking the netcheck output:
- Is there at least one configured STUN server,
- Can we reach all configured STUN servers,
- Does the address detected by STUN vary by STUN region (Hard NAT)