Add websocket paths including relay to nginx template

[lixmal]

Describe your changes

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Checklist

• Is it a bug fix
• Is a typo/documentation fix
• Is a feature enhancement
• It is a refactor
• Created tests that fail without the change (if possible)

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Documentation

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Paste the PR link from https://github.com/netbirdio/docs here:

netbirdio/docs#439

[Copilot]

Pull Request Overview

This PR adds websocket support to the nginx configuration template by introducing a new relay upstream and adding websocket-specific headers to existing and new proxy locations.

• Added relay upstream configuration pointing to port 33080
• Added websocket headers (Upgrade, Connection, Host) to signal and management ws-proxy endpoints
• Added new /relay location with websocket support

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud