Draft Spec for Cascading Default + User Settings (#1258)

* Start working on drafting this spec

* Really add a LOT of notes

* More spec updates.

  * Remove `hiddenProfiles` in favor of `profile.hidden`
  * Add info on how layering will work
  * add more powershell core info

* Finish remaining TODO sections

* Apply suggestions from code review

Fix simple typos

Co-Authored-By: Dustin L. Howett (MSFT) <duhowett@microsoft.com>

* Lots of feedback from PR

  * Try and make dynamic settings a bit clearer
  * more clearly call out serializing only what's different from a default-
    constructed `Profile`
  * Add more goals
  * add a blurb for user-default profile objects

* Add updates concerning dynamic profile generation (#1321)

* Add updates concerning dynamic profile generation

  This is based on discussion with @DHowett-MSFT we had o*line. We're trying to
  work through a way to prevent dynamic profiles from roaming to machines the
  dynamic profiles might not exist on.

  After writing this up, I'm not totally sure that it's a better design.

* Add some initial updates from discussion

* Pushing some updates here. I haven't given it a once over to ensure it's all consistent but it's worth reviewing @DHowett-MSFT

* Some minor updates from Dustin

* Fix a bunch of slightly more minor points in the spec

* Move "Profile Ordering" to "Future considerations"

* Add some notes on migrating profiles, GUID generation, de-duping profiles, and O R A N G E

* Fix the indenting here

* Update powershell core to be a dynamic profile, don't even mention other options.

* Remaining PR feedback

* Apply suggestions from code review

Co-Authored-By: Michael Niksa <miniksa@microsoft.com>

* remove a dead comment