Migrate Copilot engine from COPILOT_CLI_TOKEN to COPILOT_GITHUB_TOKEN with backward compatibility#3138

pelikhan merged 6 commits intomaingithubnext/gh-aw:mainfrom

copilot/update-copilot-cli-tokengithubnext/gh-aw:copilot/update-copilot-cli-tokenCopy head branch name to clipboard