Add a gas mode to Swapscout

## What to do? 

We need to add one additional mode to Swapsciout - "Get gas" mode

More details on the Notion task: https://www.notion.so/blockscout/b4b4eb6b579048cbb22c52f794537832?v=1c07091d838743c99a710a4e83f34117&p=2533d73641f880e0ad87f8937a81c5c2&pm=c