Coretime Feature branch (relay chain) (#1694)

Also fixes: https://github.com/paritytech/polkadot-sdk/issues/1417

- [x] CoreIndex -> AssignmentProvider mapping will be able to change any
time.
- [x] Implement
- [x] Provide Migrations
- [x] Add and fix tests
- [x] Implement bulk assigner logic
- [x] bulk assigner tests
- [x] Port over current assigner to use bulk designer (+ share on-demand
with bulk): top-level assigner has core ranges: legacy, bulk
- [x] Adjust migrations to reflect new assigner structure
- [x] Move migration code to Assignment code directly and make it
recursive (make it possible to skip releases) -> follow up ticket.
- [x] Test migrations
- [x] Add migration PR to runtimes repo -> follow up ticket.
- [x] Wire up with actual UMP messages
- [x] Write PR docs

---------

Co-authored-by: eskimor <eskimor@no-such-url.com>
Co-authored-by: Bradley Olson <34992650+BradleyOlson64@users.noreply.github.com>
Co-authored-by: BradleyOlson64 <lotrftw9@gmail.com>
Co-authored-by: Anton Vilhelm Ásgeirsson <antonva@users.noreply.github.com>
Co-authored-by: antonva <anton.asgeirsson@parity.io>
Co-authored-by: Bastian Köcher <git@kchr.de>
Co-authored-by: Marcin S. <marcin@realemail.net>
Co-authored-by: Bastian Köcher <info@kchr.de>
Co-authored-by: command-bot <>

prdoc/pr_1694.prdoc

@@ -0,0 +1,24 @@
+# Schema: Polkadot SDK PRDoc Schema (prdoc) v1.0.0
+# See doc at https://raw.githubusercontent.com/paritytech/polkadot-sdk/master/prdoc/schema_user.json
+
+title: Agile Coretime Base Relaychain Functionality
+
+doc:
+  - audience: Runtime User
+    description: |
+      The relay chain is now capable of receiving assignments from the coretime
+      chain and will schedule parachains and on-demand orders accordingly.
+      Existing leases and system chains are preserved. They get a reserved
+      coretime core via a migration. 
+migrations: 
+  db: []
+  runtime: 
+    - reference: polkadot-runtime-parachains
+      description: |
+        Claim queue in scheduler now no longer contains Option values and
+        assignments now contain information necessary to accomodate for coretime
+        features. Also all existing parachains are converted to coretime
+        assignments.
+
+crates:
+  - name: polkadot-runtime-parachains