[WIP] Add features.copilot-requests to enable Copilot integration

[Copilot]

• Explore codebase to understand structure
• Add CopilotRequestsFeatureFlag constant in pkg/constants/constants.go
• Add PermissionCopilotRequests scope in pkg/workflow/permissions.go
• Skip secret validation step when copilot-requests feature is enabled in copilot_engine_installation.go
• Add copilot-requests: write permission in compiler_activation_jobs.go buildMainJob()
• Pass ${{ github.token }} instead of ${{ secrets.COPILOT_GITHUB_TOKEN }} in copilot_engine_execution.go when feature is enabled
• Update GetRequiredSecretNames in copilot_engine.go to exclude COPILOT_GITHUB_TOKEN when feature is enabled
• Add tests in copilot_requests_feature_test.go
• Address code review feedback
• Run CodeQL security check (no issues found)

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