CLI in TTL config is not clear

[Jennifer88huang-zz]

Is your enhancement request related to a problem? Please describe.

Not quite understand what does "N/A", "100" mean in a separate CLI in https://pulsar.apache.org/docs/en/next/admin-api-namespaces/#configure-message-ttl

Is it the returned value?

Describe the solution you'd like
Give clear and concise description for the above values.

[Jennifer88huang-zz]

@sijia-w could you like to investigate and try to fix the issue? Thank you.

[sijia-w]

@jennifer88huang I checked this page https://pulsar.apache.org/docs/en/cookbooks-retention-expiry/#clear-backlog and the N/As seem to be empty returned messages. If they are not, I will update my changes accordingly.