OpenAI_2.1.0-beta.1

What's Changed

• Remove prerelease switch from NuGet instructions by @joseharriaga in https://github.com/openai/openai-dotnet/pull/235
• 2.1.0-beta.1 staging: RealtimeConversationClient by @trrwilson in https://github.com/openai/openai-dotnet/pull/238
• 2.1.0-beta.1: CHANGELOG and release snap by @trrwilson in https://github.com/openai/openai-dotnet/pull/239

Full Changelog: https://github.com/openai/openai-dotnet/compare/OpenAI_2.0.0...OpenAI_2.1.0-beta.1