MEV-Boost Direct builder connection

Currently, relays are in a critical path as bids flow from builders to proposers. This adds a little latency and places relays in a (permissioned) position to significantly impact the functioning of the (permissionless) block auction. However, looking at optimistic relaying, we see that relays often don't need to be in this privileged position.

I wrote a small proposal for how MEV-Boost could be changed to skip relays where they are not necessary by first querying information about optimistic builder endpoints and then interacting with those directly. This change does not require CL or EL changes.

More details [here](https://collective.flashbots.net/t/mb-direct-an-idea-for-mev-boost-improvement/3350?u=quintus)