Taskgraph init should generate configs that are compatible with org level grants #718

We set up some basic scopes for any repo in an org, with the intent of helping folks get setup with TC as quickly as possible. I was playing around with this and realized the index routes and caches we use by default in taskgraph init aren't compatible with this setup. Seeing as both the org level repos and taskgraph init are aimed at making things easy for newcomers, we should make sure these two features work together out of the box.

Here's what I had to change starting from a fresh taskgraph init:
https://github.com/mozilla-releng/org-scope-test/compare/7b8ace554506cba9ea199b490c7b44cce017871d..60add700bd573a8e822a384ba18a40942661c725

This will depend on the org (only mozilla and mozilla-releng are supported atm), and will be different if a trust project is specified. As taskgraph init will have no way of knowing how things are configured in fxci-config, we'll need some context provided by the user on whether the configuration has a trust project defined or not (perhaps it should default to not?)