[builder] [consider] submit v0.6 & v0.7 bundles in the same transaction #1066

Describe the feature
In Rundler v0.7 we introduced a multicall3 dependency for key funding. We can use this same dependency to submit multi-bundles targeting multiple entry points at the same time.

This reduces the amount of signers that we need by 1/2 currently and lets this scale to more entry points in the future.