GH Copilot: Add setup steps

[orestisfl]

Summary of your changes

See https://docs.github.com/en/copilot/how-tos/use-copilot-agents/coding-agent/customize-the-agent-environment#preinstalling-tools-or-dependencies-in-copilots-environment for reference.

This will avoid permission errors when Copilot tries to download hermit/go packages.

[Copilot]

Pull Request Overview

This PR adds a GitHub Copilot setup workflow to preinstall tools and dependencies in Copilot's environment, preventing permission errors when Copilot tries to download hermit/go packages during code assistance.

Key changes:

• Creates a new GitHub workflow specifically for Copilot setup steps
• Configures hermit environment initialization and package downloads
• Sets up proper permissions and triggers for the workflow

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