Improve JSONB object conversion from HAF binary operation storage

The following discussion from !201 (merged) should be addressed:

• @bwrona started a discussion:

  Here we can eliminate fc::variant and next variant_object processing while building jsonb represenation. Instead, we should deserialize hive::protocol::operation and visit it using proper visitor building target jsonb representation. Such solution should provide fastest way to convert hive::protocol::operation into json representation