gocb SDK docs should provide examples how to configure connection string based configs

There are several configs that can be changed in the gocb SDK that do not have direct accessible variables from the code. These need to be set with the URL, for example "config_poll_interval". These settings are listed here https://github.com/couchbase/gocbcore/blob/v7/agent.go#L154. We should probably list them in the docs (mentioned the unit used) and explain how to configure with the URL/connection string. This can possibly go to: https://docs.couchbase.com/go-sdk/1.5/client-settings.html