[web][tests] Added package to fix tests

Summary:
Added identity-obj-proxy as discussed here: https://linear.app/comm/issue/ENG-2654/problems-with-jest
That's the way to deal with .css imports in tested .js files. Usually .js files contains utility that shouldn't import
css, but sometimes they do and that's what failed after yarn test in web.
After installing that and some modifications in jest config it works.
Addign @ashoat as a reviewer as I added deps. At some point we may want to add it in other directories too, if we'll need to ignore some imports.

Test Plan: Runned yarn test in web. Worked and tests passed instead of crashing.

Reviewers: tomek, ashoat, atul

Reviewed By: ashoat

Subscribers: atul, ashoat, tomek

Differential Revision: https://phab.comm.dev/D6230