[nix] Create new url facts

Summary:
Part of ENG-5153
Depends on D9397

We would like to separate hosting web app on dev environment to localhost:3000/webapp/ and move the keyserver logic to localhost:3000/keyserver/ (so in the end nothing will be hosted on localhost:3000/) to simplify the dev environment and allow for web <-> keyserver separation. We can also use this opportunity to cleanup the naming. This diff automatically adds new files on nix start. They will be used in the later diff.

Production will need to be updated so that keyserver_url.json contains data from squadcal_url.json and webapp_url.json contains data from commapp_url.json

Test Plan: Run nix develop, check if files are generated

Reviewers: inka, kamil, atul, ashoat

Reviewed By: kamil, ashoat

Subscribers: ashoat, tomek, wyilio

Differential Revision: https://phab.comm.dev/D9398