Added Polkadot <> Kusama bridge configuration (#108)

This PR adds bridge configuration to allow exchanging assets between
Polkadot and Kusama Asset Hubs. So far we only support sending KSM from
Kusama Asset Hub to Polkadot Asset Hub as wKSM + DOT from Polkadot Asset
Hub to Kusama Asset Hub as wDOT. Other assets may be added later.

The opposite direction is also supported, though it'll need dependencies
upgrade to >= v1.4.

---

Similar Rococo <> Westend bridge is also active on live chains. You may
read docs on how to play with it here:
https://github.com/paritytech/polkadot-sdk/blob/master/cumulus/parachains/runtimes/bridge-hubs/README.md

For Polkadot <> Kusama bridge we have a dedicated branch for local
zombienet tests:
https://github.com/svyatonik/runtimes/tree/sv-pk-bridge-with-zombienet-tests.
You may run autotests (exchanging assets) there - see
https://github.com/svyatonik/runtimes/blob/sv-pk-bridge-with-zombienet-tests/system-parachains/bridge-hubs/zombienet/README.md
for details. You may do manual tests by spawning local chains using
those scripts and use
https://github.com/svyatonik/runtimes/blob/sv-pk-bridge-with-zombienet-tests/system-parachains/bridge-hubs/zombienet/scripts/bridges_kusama_polkadot.sh
script to run various commands - i.e. send assets manually. Polkadot js
apps is also supported.

---------

Co-authored-by: Branislav Kontur <bkontur@gmail.com>
Co-authored-by: Bastian Köcher <git@kchr.de>

CHANGELOG.md

@@ -27,6 +27,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 - Treasury is able to spend various asset kinds ([polkadot-fellows/runtimes#87](https://github.com/polkadot-fellows/runtimes/pull/87))
 - Add BEEFY to Polkadot ([polkadot-fellows/runtimes#65](https://github.com/polkadot-fellows/runtimes/pull/65))
 - Fellowship Treasury pallet on Polkadot Collectives ([polkadot-fellows/runtimes#109](https://github.com/polkadot-fellows/runtimes/pull/109))
+- Added Polkadot <> Kusama bridge to support asset transfers between Asset Hubs ([polkadot-fellows/runtimes#108](https://github.com/polkadot-fellows/runtimes/pull/108))
 
 ### Fixed