add option for generic N1qlParams

To avoid needing to change the N1qlParam if a future parameter is added, consider adding a simple String, JSON way of appending N1qlParams in addition to the current class defined params. This may be useful if a future version adds an option and we want to enable that with an older SDK.

This may also allow for passing params that are volatile/uncommitted and undocumented. There are already several such params in the N1QL Query API Request Parameters that aren't in the documentation on developer.couchbase.com.