Add option to use different relay for simulation

[onbjerg]

Adds the option to set a different relay URL for bundle simulations.

The relay URL can also be a node that implements the eth_callBundle remote procedure call.

[ChainsightLabs]

Can we branch this into the main branch :)

[gakonst]

@onbjerg any reason for us to not merge this?

[onbjerg]

Not really, I put it off because I was planning a bigger rewrite but that is still on the backburner

[gakonst]

The infamous one year PR lol kudos