[web] Allow other types of icons in menu item

Summary:
Currently, we allow only SWMansionIcons and provide them through their name. A design for invite links requires an icon which isn't a part of this set. This diff allows using any other icon, especially any svg.

Depends on D8294

Test Plan: Check if the items are still displayed correctly.

Reviewers: bartek, kamil, inka

Reviewed By: inka

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D8306