allow orders where the sell token is also the buy token #3858
Description
Why?
This would effectively turn cow protocol into a transaction relayer. So a user who only wants to have some transaction executed could create an order selling USDC for less USDC and just add that transaction as a pre-hook to their order.
This would make executing transaction gas less (i.e. not ETH required because the solver will pay the ETH and take some of your sell tokens for the service).
A prime use case for this is using cow protocol to bridge funds. Bridging is currently implemented as a post hook that runs after your order gets executed. But because we enforce that sell and buy tokens have to be different the least overhead a user can incur for executing a bridging operation is probably cheaply converting 1 stable coin into another.
If we allow orders where sellToken == buyToken we can build a very simple integration that allows bridging to all the chains that were integrated for the "swap and bridge" feature.
For reference this was already done as a proof of concept during a hackathon here.