couchbase-connector - add a version of get that also returns cas and a version of replace that uses cas

[adrianfilip]

Context

• We want to add a versions of get that also return cas and a version of replace that uses cas. That way we can do smth like 'getWithCas >>> process >>> replaceWithCas'.
• https://docs.couchbase.com/java-sdk/current/howtos/concurrent-document-mutations.html