[server] Add source message column to db

Summary: In D592 we forgot to add the column to a script which creates db. Karol encountered the error when setting up the environment.

Test Plan: The change is so simple, I haven't tested it.

Reviewers: ashoat

Reviewed By: ashoat

Subscribers: KatPo, zrebcu411, Adrian, atul, subnub

Differential Revision: https://phabricator.ashoat.com/D635