Add uml diagram of different process interactions

[samlaf]

Was not familiar with the mev-share codebase, so took me a little while to figure out what's going on in this repo. Figured it would be super useful to add a UML diagram of the different requests being made. Came up with this, let me know if it's accurate:

In light of this diagram, one thing I don't understand with this architecture, is how the preconf-operator is able to give preconfs if all it is receiving is a txHash. I don't understand how notifyHint is supposed to work with preconfing. It seems like they aren't compatible, and the only way for the preconf-operator to give a preconf is if it receives the entire tx early, such that it can execute it. Otherwise it can only give inclusion preconfs.