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 <>

polkadot/zombienet_tests/smoke/0004-coretime-smoke-test.zndsl

@@ -0,0 +1,19 @@
+Description: Bulk core assignment Smoke
+Network: ./0004-coretime-smoke-test.toml
+Creds: config
+
+alice: is up
+coretime-collator: is up
+
+alice: reports block height is at least 3 within 30 seconds
+# configure relay chain
+alice: js-script ./0004-configure-relay.js with "" return is 0 within 600 secs
+
+# Wait 2 sessions. The parachain doesn't start block production immediately.
+alice: log line contains "New session detected session_index=2" within 600 seconds
+
+# configure broker chain
+coretime-collator: js-script ./0004-configure-broker.js with "" return is 0 within 600 secs
+
+# TODO: Fix this
+# alice: parachain 100 block height is at least 10 within 600 seconds