OpenAI_2.0.0

What's Changed

• Prepare 2.0.0 release (Part 1) by @joseharriaga in https://github.com/openai/openai-dotnet/pull/233
• Prepare 2.0.0 release (Part 2) by @joseharriaga in https://github.com/openai/openai-dotnet/pull/234

Full Changelog: https://github.com/openai/openai-dotnet/compare/OpenAI_2.0.0-beta.13...OpenAI_2.0.0