cumulus: add asset-hub-rococo runtime based on asset-hub-kusama and add...

cumulus: add asset-hub-rococo runtime based on asset-hub-kusama and add asset-bridging support to it (#1215)

This commit adds Rococo Asset Hub dedicated runtime so we can test new
features here, before merging them in Kusama Asset Hub.
Also adds one such feature: asset transfer over bridge (Rococo AssetHub
<> Wococo AssetHub)

- clone `asset-hub-kusama-runtime` -> `asset-hub-rococo-runtime`
- make it use Rococo primitives, names, assets, constants, etc
- add asset-transfer-over-bridge support to Rococo AssetHub <> Wococo
AssetHub

Fixes #1128

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Co-authored-by: Branislav Kontur <[email protected]>
Co-authored-by: joe petrowski <[email protected]>
Co-authored-by: Francisco Aguirre <[email protected]>