[Polkadot] [Wallet] update polkadot coins to show the correct logo (#37030)

Update the Polkadot Westend coins to display the associated Polkadot logo
instead of a default icon.

We need to manually add Westend Asset Hub as a supported testnet to get it
properly display as a testnet network.

components/brave_wallet_ui/options/asset-options.ts

@@ -70,6 +70,7 @@ export const getNetworkLogo = (chainId: string, symbol: string): string => {
     case 'ADA':
       return CardanoIcon
     case 'DOT':
+    case 'WND':
       return PolkadotIcon
   }