Improve price impact display when we don't have price for any of the assets

[greg-nagy]

• [ ] verify theory: sellTokenToEthRate or buyTokenToEthRate is 0 in the 0x quote api response, when we can't resolve USD or ETH price for an asset from coingecko
• [ ] (if theory correct) check sellTokenToEthRate and buyTokenToEthRate if it's 0 in the 0x quote response and inform the user that we don't know about the price impact
• [ ] handle error from the price fetching and inform the user if that happens

[0xDaedalus]

I wonder if we can greatly simplify this whole thing by using the expectedSlippage response from 0x?

[greg-nagy]

I ran a few tests, and based on that:

• the expectedSlippage is always null — tested on optimism and mainnet, with multiple pairs and couldn't find one which is not null
• 0x price api result has a estimatedPriceImpact property and it returns the value of the price impact displayed on matcha as a string
  • note: in some cases eg OP<>0XBTC swap on optimism the estimatedPriceImpact is 0 meanwhile we get price data from coingecko

Additional observation from #2236 and #2449:

• in certain cases sellTokenToEthRate and buyTokenToEthRate is populated even if we don't get price data from coingecko. Eg. optimism OP<>sBTC
• in that particular case estimatedPriceImpact is 0 > I think this signals that they don't have data