Synchronous Replication snippet

Please add a Sync Rep-style durability section to the Java Sub-Doc page, along the lines of
https://docs-staging.couchbase.com/dotnet-sdk/3.0/howtos/subdocument-operations.html#durability
https://github.com/couchbase/docs-sdk-dotnet/blob/release/3.0alpha/modules/howtos/pages/subdocument-operations.adoc