Feature(new_metrics): migrate server-level metrics for nfs

[empiredan]

nfs metrics will be in use once nfs_node (nfs_node.cpp) is created, which is a member of replica_stub. Thus in new framework all of them will be attached to server entity. Related source files and metrics are listed as below.

nfs_client_impl.cpp:

Variables	Types/Computations
_recent_copy_data_size	increase(Counter)
_recent_copy_fail_count	increase(Counter)
_recent_write_data_size	increase(Counter)
_recent_write_fail_count	increase(Counter)

nfs_server_impl.cpp:

Variables	Types/Computations
_recent_copy_data_size	increase(Counter)
_recent_copy_fail_count	increase(Counter)