Integrate arax ranker

[chunyuma]

Hi @maximusunc and @dkoslicki,

This PR is created to integrate ARAX ranker into the Shepherd main branch.

Thanks to help from Max, the ARAX ranker was tested within the Shepherd system and approved to work.

[chunyuma]

Hi @maximusunc,

I noticed that some Black-formatted and tox tests failed. After checking the errors, it seems they are unrelated to the newly added worker for the ARAX ranker. For example,

• The Black complains "/home/runner/work/shepherd/shepherd/workers/merge_message/worker.py".
• The tox complains "ModuleNotFoundError: No module named 'pkg_resources'.

So can I assume these issues are expected and ignore them when merging this PR into the main branch? Thank you!