Benchmark support

[Fuuzetsu]

We may want some benchmark support. Some ideas:

• benchmarks that produce HTML/json/whatever: think criterion outputs
• it could just be a haskell_binary with some bazel tag we pick that identifies it as a benchmark: at the very least the user can ask bazel to list/run all rules with the tag then.

I think we definitely should just start with haskell_binary alias with a rule tag.

[thufschmitt]

At novadiscovery, we use a haskell_test for that, with a special benchmark tag which is excluded by default, so that bazel test //... won't run the benchmarks and bazel test //... --test_tags_filter=benchmark will run all of them.

To keep the outputs, we use a custom criterion runner (i.e. a wrapper around Criterion.defaultMain) which puts all the outputs under $TEST_UNDECLARED_OUTPUTS_DIR, so that they are available after under bazel-testlogs/my/target/test.outputs/result.{html,csv,json}

That woks quite well for us, though that require some specific setup inside the repository (a test --test_tag_filters=-benchmark in .bazelrc and a library exporting the custom runner).