Execute contract benchmarks on CI

[xermicus]

We need a CI workflow which executes the benchmarks (make bench) on our reference bench-marking hardware.

Additionally, the output from the code_size integration test should also be considered since this is an important metric.

I'd like to have this workflow executed after all other jobs finished and post the benchmark results (diffed against master) as a PR comment.

A follow up issue will be to create more benchmarks that focus on more realistic examples.

[athei]

A follow up issue will be to create more benchmarks that focus on more realistic examples.

I think the plan is that those realistic benchmarks will live in https://github.com/paritytech/evm-test-suite. There is nothing stopping us from also using those tests as benchmarks.

[xermicus]

Ah yes thanks for clarifying it, that was the idea. See also #199 - the same benchmark cases can just be used for both, regression testing on compilation and contract runtime performance.

[athei]

Yeah I guess we can also measure the compilation time there. The tests are already there. We just need to start measuring.