[web] Update type field in DB Media struct

Summary:
This is just to make flow happy in the later diffs. This is safe because we know that we will be the only ones to store Media types in the db so we can be sure that the data that we get back has more specific type.

Depends on D11535

Test Plan: flow, tests

Reviewers: kamil, marcin

Reviewed By: kamil

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D11536