CI benchmarks test

[serg-temchenko]

• - To catch bugs with benchmarks in Substrate, it is also required to run a simple pass on benchmarks, e.g. ./target/debug/polka-storage-node benchmark pallet --pallet "" --extrinsic "" --steps 2 --repeat 1

Still to be implemented when we will have some pallets to test.

Related to #3.

[jmg-duarte]

With benchmarks v2 cargo test --features runtime-benchmarks -- benchmark or something very similar should be enough, I'll add this to our CI in the upcoming benchmark PRs