[keyserver/web/desktop] Add macos and windows as platforms

Summary: We want to support desktop device types to be able to handle native notifications. This diff adds macos and windows to the possible platform and sets config on the web app depending on where it's running. Older desktop clients with newer web app will still be treated as web. Additionaly if on the socket initialization we detect that someone has a user agent with "Electron" and still has device token of web we will ask the web app to send us the current device type, so already logged in users will be updated.

Test Plan:

• check that after login the device type is macos
• check that for already logged in users the device type changes to macos and remains that after logging out on the anoonymous cookie

Reviewers: tomek, inka, kamil, ashoat

Reviewed By: ashoat

Subscribers: ashoat, atul

Differential Revision: https://phab.comm.dev/D6889