Refactor replication code (#1507)

* refactor: Split redis I/O logic out of dfly::Replica

* Split DFLY shard replication into a separate class.

* Address comments from CR

* Add comments

* remove dead code

* Add a virtual dtor

* * Address comments by Shahar.
* Fix the redis replication code.

* And now fix the Dragonfly replication

src/server/main_service.h

@@ -21,7 +21,6 @@ namespace dfly {
 class Interpreter;
 class ObjectExplorer;  // for Interpreter
 using facade::MemcacheParser;
-
 class Service : public facade::ServiceInterface {
  public:
   using error_code = std::error_code;