Implement translation of media JSON object to SQLite database entities

Summary: This diff introduces a function to convert folly dynamic thet represents media JSON object received with notification into SQLite database Media enitities.

Test Plan: No testing plan. Future diffs will provide a code that uses those functions on iOS and Android respectively

Reviewers: palys-swm, karol-bisztyga

Reviewed By: palys-swm, karol-bisztyga

Subscribers: ashoat, Adrian, atul, yayabosh

Differential Revision: https://phab.comm.dev/D3982