Hello containerd people,

By browsing the client's code, i saw a harded coded message like
errors.New("no grpc connection or services is available")

My idea is to centralize hard coded messages in a logic like enum.

The advantage of doing that:

• To increase the code readability and the maintainability
• Constants consistently, expressively and type-safe
• Sharing common behavior
• Easy to make internationalization if we want to support other language in the futur

If your ok. We should think how to avoid the negative pressure on this enum if it will be called by many objects as a client.