allow to store configPath in thrift server's metadata
allow to store configPath in thrift server's metadata

Summary: Added metadata object to keep some data associated with the server.

Reviewed By: andriigrynenko

Differential Revision: D24089524

fbshipit-source-id: 0f87a18054de67952706ddc67157169da2ce910b

facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift