Add github benchmark action

[mkannwischer]

This adds benchmark visualization using https://github.com/benchmark-action/github-action-benchmark.

When ever a new commit is pushed to the main branch, it will upload the benchmarks to the https://github.com/pq-code-package/mlkem-c-aarch64/tree/gh-pages branch and they will be visualized at https://pq-code-package.github.io/mlkem-c-aarch64/dev/bench.

This won't run on PRs (and it can't because these workflow runs won't have the permission to push commits -- see my comment below), so we can only see if it works the way it is intended if we merge it.

I have performed extensive tests here: https://github.com/mkannwischer/bench-test
And you can see how it should look like here: https://mkannwischer.github.io/bench-test/dev/bench/

[mkannwischer]

After lots of experimenting, I figured out that we cannot test this in a pull request.

The maximum permission of the GITHUB_TOKEN in pull requests from forks on contents in the repo is read, but we need write to be able to create commits in the gh-pages branch. In the end we want to only run it on the main branch, so that's not a problem in the end.

See: https://docs.github.com/en/actions/security-guides/automatic-token-authentication#permissions-for-the-github_token

I have performed quite some tests in https://github.com/mkannwischer/bench-test today, and I believe that what we have here right now should work.

[hanno-becker]

Minor comments, otherwise LGTM