integration tests: add more emulated bridge tests (#7576)

Add emulated e2e tests for following scenarios:

Exporting native asset to another ecosystem:
- Sending WNDs from Penpal Westend to Penpal Rococo: PPW->AHW->AHR->PPR
- Sending WNDs from Westend Relay to Penpal Rococo: W->AHW->AHR->PPR
   Example: Westend Treasury funds something on Rococo Parachain.

Importing native asset from another ecosystem to its native ecosystem:
- Sending ROCs from Penpal Westend to Penpal Rococo: PPW->AHW->AHR->PPR
- Sending ROCs from Penpal Westend to Rococo Relay: PPW->AHW->AHR->R
   Example: Westend Parachain returns some funds to Rococo Treasury.

Signed-off-by: Adrian Catangiu <adrian@parity.io>