Snowbridge on Westend (#5074)

### Context

Since Rococo is now deprecated, we need another testnet to detect
bleeding-edge changes to Substrate, Polkadot, & BEEFY consensus
protocols that could brick the bridge.

It's the mirror PR of https://github.com/Snowfork/polkadot-sdk/pull/157
which has reviewed by Snowbridge team internally.

Synced with @acatangiu

 about that in channel
https://matrix.to/#/!gxqZwOyvhLstCgPJHO:matrix.parity.io/$N0CvTfDSl3cOQLEJeZBh-wlKJUXx7EDHAuNN5HuYHY4?via=matrix.parity.io&via=parity.io&via=matrix.org

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Co-authored-by: Clara van Staden <[email protected]>