Lua: global table to store state between threads

*Description*:
Lua state is per worker and it will be non-trivial/impossible to share it between threads. A global storage for Lua is to provide a Lua API that wraps a metadata/table that calls into C++ code with proper locking to set/get items in a global table. All Lua code can access global table and share state in different Envoy Lua filters.

The original request is from #4008