Run go-bencher in CI

[ethanfrey]

Follow up from #635

There are now some decent benchmarks we can run locally for Cw20 vs native transfers.
We also run them in a CI job, but that is not the best benchmark.

Let's move these comparisons (cw20 vs bank, not all the gas pricing stuff) to go-bencher for better metrics there.

After that is integrated we can look at comparing more complex CosmWasm contracts with more complex modules.