Make kwenta able to pay for gas on L2

[gberg1]

Summary

Dev Tasks

• Gas price to be read from the provider
• Mainnet - notify user that they have no WETH on L2 and point them to the optimism dapp bridge (blocked by Optimism link)
• Add constant to mono repo for gas
• Ping Erika to figure out best way to show this (header or when they make a transaction)
• Use gas estimate for L2

Airdrop WETH to L2 users, ping @ajsantander choose who is eligible

Gas Price - on L1 keep same logic, recommended and custom fetched from 3rd party api. On L2 GWEI will be a gas price of 1

gas estimate for L2 is going to be hardcoded to 9M, gas estimate for L1 still use gas limit estimate func

QA Tasks

• PR: feat: prompt user to get eth for gas if has none #305
• Go to https://kwenta-git-l2-get-weth-synthetixio.vercel.app/exchange
• Connect wallet
• Switch to Optimism Mainnet
• Expected to see a Your wallet has no Synths. Buy sUSD to trade Synths: message in the footer.
• Switch to Optimism Kovan or Mainnet.
• Expect the message to disappear. Optimism Kovan doesn't need gas.

[kelonye]

Hard-coded the gas prices (see below) to zero for now. Asked if there will be an endpoint that will allow us to get these prices, in the optimism channel.

[kelonye]

Updating this to read from provider.getGasPrice