request: Add mock-only mode to the MEV possible configs

[marioevz]

Right now there is Full-MEV and Mock-MEV modes, and I'm using Mock-MEV mode to debug the Deneb update to the Mock-builder, however this mode places mev-boost in-between the consensus client and the mock-builder, which is fine for a normal test, but it's made debugging the mock-builder quite hard since mev-boost rejects the payloads the mock-builder produces for a number of reasons.

It would be nice to have a third option just for debugging purposes where the Consensus client is connected directly to the mock-builder and skips the mev-boost entirely.

I reckon this could result in a chicken-and-egg problem because the mock-builder requires the CL and the EL IP addresses, but the Mock-builder IP address itself must be included in the builder flag of the CL.

[h4ck3rk3y]

Hey! @marioevz what do you think about opening a PR to add a flag that skips the mev-boost for mock builder entirely, maybe its a third mev-type? Regarding the chicken and egg problem, service names can be used instead of IP addresses and the service names can be guessed before hand especially for services like mock-mev