[web] Make identity service client runnable on shared worker

Summary:
[ENG-6766 : Move IdentityServiceClientWrapper to shared worker](https://linear.app/comm/issue/ENG-6766/move-identityserviceclientwrapper-to-shared-worker)

Currently IdentityServiceClientWrapper has two things which don't work on the shared worker:

• getConfig which is registered only in browser window js context and not worker
• opaque WASM path needs to be different on webworker (because the inner fetch base origin is different)

this diff changes both of these values to constructor arguments instead of using global context.

Depends on D11272

Test Plan: Make sure logging in to the identity service still works.

Reviewers: kamil, tomek

Reviewed By: kamil

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D11273