Test: Add proxy support to the fetch defined by node

[chrmarti]

Refs: #228697

• macOS @legomushroom
• linux @DonJayamanne
• windows @deepak1556

Complexity: 4

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Add the following user setting to make Copilot Chat use Node.js' fetch and reload the window:

"github.copilot.advanced.debug.useElectronFetcher": false

Clone https://github.com/microsoft/vscode-proxy-agent.git and follow https://github.com/microsoft/vscode-proxy-agent/blob/main/.devcontainer/basic-auth-test/README.md to test the proxy support for Node.js' fetch.

Do some testing of Copilot Chat with the two proxies from above. Sign out and back in. Run a few chat requests.