Run benchmarks on every PR

[xThaid]

The motivation is that performance changes should be visible by default (as opposed to manually triggering the benchmarks).

• When benchmarks are run on the master, the results will be saved to the cache.
• On PRs with benchmark label, benchmarks are run and compared to the base branch as the baseline.
• Metrics are now exposed to Github job summary, so one doesn't have to search through logs.

I am not adding benchmark label, as the job will fail. Most likely we need to merge this first, so permissions are propagated correctly. Here is the preview: https://github.com/xThaid/coreblocks/pull/2#issuecomment-2054193764

Fixes #657.

[xThaid]

I removed benchmark label as it will trigger the job that issues a comment in this PR, which will fail due to lack of permissions. I believe that putting this modified workflow on the master branch should solve permission issues.