[desktop] Handle macos notifications

Summary: Register for push notifications and handle them by displaying a native notification. When a user clicks the notification we either navigate to the corresponding chat or if there is no main windows open a new one with a correct url.

Test Plan:

• Check if the notifications display and navigate to a chat when clicked
• Check if the app is closed notifications show up and open up a new window when clicked
• Check if we get the notification but then close the app and the other way around, the click action still works correctly

Reviewers: tomek, inka, kamil

Reviewed By: tomek

Subscribers: ashoat, atul

Differential Revision: https://phab.comm.dev/D6894