Snowbridge: Update Bridge Pricing Parameters to Lower Transfer Fees

When Snowbridge was launched the transfer fees were calculated based on the following parameters which reflected market conditions at the time:

• Worst Case Gas price: 60 Gwei
• ETH:DOT exchange rate: 1:450

This resulted in price in the following prices: 

• 11.456568 DOT to transfer from Polkadot to Ethereum.
• 0.000399 ETH to transfer from Ethereum to Polkadot.

This proposal will change the pricing parameters to:

• Worst Case Gas price: 25 Gwei
• ETH:DOT exchange rate: 1:566

Resulting in the following fees:

• 6.1278015332 DOT to transfer from Polkadot to Ethereum.
• 0.000317 ETH to transfer from Ethereum to Polkadot.

Old Pricing Params:

setPricingParameters({
    exchangeRate: 2,222,222,222,222,222
    rewards: {
        local: 100,000,000
        remote: 250,000,000,000,000
    }
    feePerGas: 60,000,000,000
    multiplier: 1,333,333,333,333,333,333
})

New Pricing Params:

setPricingParameters({
    exchangeRate: 1,766,784,452,296,820
    rewards: {
        local: 100,000,000
        remote: 250,000,000,000,000
    }
    feePerGas: 25,000,000,000
    multiplier: 1,333,333,333,333,333,333
})