Test performance for calls into contracts

[webmaster128]

To get an idea what it costs to call into a contract.

In the CI and my machine this takes roughly twice the time of the "Combined/get instance from memory cache and execute" benchmark in cosmwasm-vm

System	cosmwasm-vm benchmark	Call from Go
Circle CI (Docker/medium)	85 µs	112 µs
My machine	44 µs	56 µs