[keyserver] Update report and upload URLs to use web.comm.app

Summary:
Either should work. Now that web.comm.app is live, let's use that.

Also moving things to be fetched inside functions so that the app doesn't immediately crash if the config isn't present.

Depends on D3975

Test Plan: Confirmed that on prod our image URLs use squadcal.org, and that I can replace it with web.comm.app and the images still load

Reviewers: atul, palys-swm

Reviewed By: palys-swm

Subscribers: Adrian, yayabosh

Differential Revision: https://phabricator.ashoat.com/D3976