Add continuous benchmarking

[2opremio]

What problem does your feature solve?

Performance degradations caused by code changes can be subtle in their cause and go unnoticed.

For instance, in https://github.com/stellar/go/pull/4178 @paulbellamy and I had to carefully manually run benchmarks which we did

Adding a CI job which compares the Go benchmark results of master against the changes being proposed in a PR will help detect degradations early.

What would you like to see?

A tool like https://github.com/knqyf263/cob integrated in our CI. The tool allows erroring when certain amount of degradation (e.g. 50% worse) is detected.

What alternatives are there?

I am sure there are other tools to do this.