add the use of username and password sgcollect_info

We should document the use of sgcollect_info to use the following arguments

--sync-gateway-username=

--sync-gateway-password=

Without these arguments, we can't collect a bunch of information, including the configuration file with persistent config. This was a change in 3.0 that made this much more important.

https://docs.couchbase.com/sync-gateway/current/sgcollect-info.html is where this is missing.