Add Couchbase benchmark/performance driver for SBK

[kmgowda]

Describe the Issue (Bug/Feature) Add the SBK driver for Couch base performance benchmarking.

To Reproduce See the steps : https://github.com/kmgowda/SBK#add-your-driver-to-sbk to add the SBK driver for Couch base Get the know the Couch base IO APIs , start from here : https://docs.couchbase.com/couchbase-lite/current/index.html

Expected behavior SBK with -class Couchbase and additional parameters should benchmark the Couchbase performance

Additional context Understand the Couch base IO APIs and use them in the SBK template driver created using steps: https://github.com/kmgowda/SBK#add-your-driver-to-sbk