[Bug] Better error message when cert not provided

[laniehei]

What are you really trying to do?

Request a better error message when a cert isn't provided when describing a namespace.

Describe the bug

The following command was run:

tctl --ns <namespace> -address <address> --tls_ca_path <ca_path> -tls_key_path <key_path> n desc

and I received the following error message:

Error: Operation DescribeNamespace failed.
Error Details: rpc error: code = Unavailable desc = connection closed before server preface received

When I provided the needed --tls_cert_path, this worked, but this was non-obvious based on the error message provided.

Minimal Reproduction

See above.

Environment/Versions

tctl version 1.16.1

Additional context

Please slack me with further questions