app: use smarter pathfinding algorithm for checkout

[mds1]

In #110 we hardcoded swap paths for known liquid token pairs. This is not ideal/robust/scalable, so a smarter pathfinding algorithm should be implemented.

The easiest way to do this is likely to use this method from the Uniswap interface

• It's written for React so we'll need to make some modifications, e.g. remove useMemo and add chainId as an input
• The interface is GPL-3.0 so we can use that code freely

[mds1]

Uniswap recently released the Auto Router for Uniswap V3. This is now preferred over the method linked in the above comment

If we also support V2 swaps (https://github.com/dcgtc/dgrants/discussions/263), we should use Uniswap's V2 routing algorithm in that case