[CommCoreModule] Add metadata table to client DB

Summary: Introduce metadata table with a name and data column. Will be used to store deviceID, publicKey, privateKey, and sessionID values needed for NewSession(...) gRPC unary call.

Test Plan: Check if table was properly created

Reviewers: ashoat, def-au1t, palys-swm, varun, karol-bisztyga, jimpo

Reviewed By: ashoat

Subscribers: Adrian, benschac

Differential Revision: https://phabricator.ashoat.com/D3155