Changed advance example to reflect set_simulation_relay and fn set_simulation_relay

[da-bao-jian]

After the 0.12.0, to simulate the bundles, users are required to call the set_simulation_relay method to set a relay endpoint, otherwise it'll be None.

Additionally, I modified the set_simulation_relay method to take one more argument relay_signer, otherwise X-Flashbots-Signature header won't be set inside of relay::request

[onbjerg]

Sorry for the delayed response, good catch, I only checked this for the middleware.

Once CI passes this is good to merge