[web] Add multimediaClassName prop to encrypted media components

Summary:
Added prop to custom encrypted media components to allow for custom styling with class name, in addition to the existing style prop.
I need this to fix ENG-3946.

Test Plan: Tested together with next diffs

Reviewers: inka, ginsu, atul, kuba

Reviewed By: atul

Subscribers: ashoat, tomek, atul

Differential Revision: https://phab.comm.dev/D7993