feat(make_idempotent): support making incr request idempotent in pegasus_server_write and replication_app_base

[empiredan]

#2197

To support idempotence, a new interface make_idempotent() is introduced and
an existing interface on_batched_write_requests() is changed for both the classes
pegasus_server_write and replication_app_base. This is different from what we
have done for pegasus_write_service and pegasus_write_service::impl, both of
which provide make_idempotent() and put() by the following PRs:

• feat(make_idempotent): support making incr request idempotent in pegasus_write_service::impl #2185
• feat(make_idempotent): support making incr request idempotent in pegasus_write_service #2192

make_idempotent() for replication_app_base is provided as a virtual function
called by primary replicas, implemented internally by pegasus_server_impl and
pegasus_server_write. on_batched_write_requests for replication_app_base
is the same. It is changed with a new parameter original_request added. It is just
the original request received from the client. It must be an atomic request (i.e. incr,
check_and_set and check_and_mutate) if it is non-null, and used to decide if a
write request is atomic and generate the response corresponding to the atomic write
request.