Allow updating KV bucket settings from add command

[kroepke]

add --[no]-update flag to add KV command

if set, the update flag will use CreateOrUpdateKeyValue instead of CreateKeyValue to allow changing settings of the bucket

Not passing the parameter retains the original behavior

[ripienaar]

Thanks for this, I think I'd rather model this around how nats stream works with a add and edit commands separate and edit only showing flags that's changeable

[kroepke]

Sure, I am happy to update this if you feel it's worth it. I just did it because I ran into wanting to update settings while testing.

[ripienaar]

Supporting updates to bucket config has been on my todo list but never got to it, so would be very grateful to see a contribution there!